Measurement control device

ABSTRACT

A measurement control device includes: a sensing unit that outputs a signal according to an air flow rate; a pulsation state calculation unit that calculates a pulsation state of pulsation generated in the air flow rate using an output value of the sensing unit; and a pulsation error correction unit that corrects the air flow rate. The pulsation state calculation unit has an upper extreme value determination unit and a frequency calculation unit. The upper extreme value determination unit cancels the upper extreme value that has presently appeared, when the output value remains to be more than a predetermined lower threshold. The upper extreme value determination unit updates the lower threshold on a basis of at least one of air flow rate, pulsation frequency, or pulsation amplitude specified on the basis of the output value.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of InternationalPatent Application No. PCT/JP2020/045682 filed on Dec. 8, 2020, whichdesignated the U.S. and claims the benefit of priority from JapanesePatent Application No. 2019-235221 filed on Dec. 25, 2019. The entiredisclosures of all of the above applications are incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a measurement control device.

BACKGROUND ART

A device for measuring an air flow rate includes an electronic controlunit, and the electronic control unit calculates the air flow rate onthe basis of an output value of an air flow sensor.

SUMMARY

A measurement control device includes: a sensing unit that outputs asignal according to an air flow rate; a pulsation state calculation unitthat calculates a pulsation state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate. The pulsation statecalculation unit has: an upper extreme value determination unit thatdetermines whether the output value has become an upper extreme value;and a frequency calculation unit that calculates a pulsation frequencyof the pulsation generated in the air flow rate on a basis of a timeinterval at which the output value becomes the upper extreme value. Theupper extreme value determination unit cancels the upper extreme valuethat has presently appeared, when the output value remains to be morethan a predetermined lower threshold during a period from a timing whenthe upper extreme value has previously appeared to a timing when theupper extreme value has presently appeared in a waveform representing atime change of the output value. Further, the upper extreme valuedetermination unit updates the lower threshold on a basis of at leastone of air flow rate, pulsation frequency, or pulsation amplitudespecified on the basis of the output value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an air flow meter according to a firstembodiment as viewed from an upstream side.

FIG. 2 is a perspective view of the air flow meter as viewed from adownstream side.

FIG. 3 is a vertical cross-sectional view of the air flow meter attachedto an intake pipe.

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3.

FIG. 5 is a cross-sectional view taken along line V-V of FIG. 3.

FIG. 6 is a block diagram illustrating a schematic configuration of theair flow meter.

FIG. 7 is a block diagram illustrating a schematic configuration of acorrection circuit according to the first embodiment.

FIG. 8 is a diagram for describing a method of calculating an intervalbetween upper extreme values.

FIG. 9 is a diagram for describing a method of calculating an averageair amount.

FIG. 10 is a diagram for describing a method of calculating a pulsationamplitude.

FIG. 11 is a diagram illustrating a relationship between pulsationcharacteristics and approximate values.

FIG. 12 is a diagram illustrating a map.

FIG. 13A is a diagram for describing a calculation method of the averageair amount after correction.

FIG. 13B is a diagram for describing determination of an upper extremevalue when a sampling value at present time remains to be more than alower threshold.

FIG. 13C is a diagram illustrating an example in which an output valueof a sensing unit becomes equal to or less than the lower threshold dueto influence of harmonics, and an upper extreme value is not canceledand is erroneously detected as the upper extreme value.

FIG. 13D is a diagram illustrating an example of a case where a steepoutput change occurs in the output value of the sensing unit and theoutput value becomes higher without becoming equal to or less than thelower threshold.

FIG. 13E is a diagram for describing a map in which a pulsationamplitude, a pulsation frequency, and an average air amount areassociated with a reference value of a lower threshold.

FIG. 13F is a flowchart of an upper extreme value determination unit.

FIG. 13G is a diagram illustrating a modification of a map.

FIG. 14 is a block diagram illustrating a schematic configuration of acorrection circuit according to a second embodiment.

FIG. 15 is a diagram for exemplifying noise contained in the outputvalue.

FIG. 16 is a diagram for describing a method of cutting a minus value ofan output value.

FIG. 17 is a block diagram illustrating a schematic configuration of acorrection circuit according to a third embodiment.

FIG. 18A is a diagram for describing a calculation method of an intervalof upper extreme values.

FIG. 18B is a diagram for describing a method of updating a lowerthreshold of an upper extreme value determination unit of a correctioncircuit according to a fifth embodiment.

FIG. 18C is a diagram illustrating how the output value and the lowerextreme value of the sensing unit of the correction circuit in the fifthembodiment change.

FIG. 18D is a flowchart of an upper extreme value determination unit ina sixth embodiment.

FIG. 18E is a diagram illustrating how the output value and the lowerextreme value of the sensing unit of the correction circuit in the sixthembodiment change.

DESCRIPTION OF EMBODIMENTS

To begin with, examples of relevant techniques will be described.

As a configuration for measuring an air flow rate, an electronic controlunit (ECU) that controls an internal combustion engine calculates an airflow rate on the basis of an output value of an air flow sensor. Inaddition to a detection signal of the air flow sensor, a detectionsignal of a crank angle sensor that detects an engine speed is input tothis ECU. The ECU calculates a pulsation frequency of the air flow rateusing the engine speed detected by the crank angle sensor, and correctsthe air flow rate using this pulsation frequency so as to reducepulsation errors, which are errors caused by pulsation of the air flowrate.

However, since the ECU performs a correction process for the air flowrate in addition to a control process of the internal combustion engine,it is assumed that a processing load of the ECU is excessivelyincreased. Accordingly, a configuration is conceivable in which thecorrection process for the air flow rate is executed by a measurementcontrol device independent of the ECU, and this measurement controldevice outputs a correction result of the air flow rate to the ECU. Inthis configuration, the ECU can acquire the correction result of the airflow rate, and moreover, the processing load of the ECU can be reduced.

However, even in this configuration, if the measurement control deviceuses the engine speed when calculating the pulsation state such as thepulsation frequency, the ECU needs to output rotation speed informationindicating the engine speed to the measurement control device. In thismanner, when the measurement control device uses the rotation speedinformation from the ECU to correct the air flow rate, there is aconcern that correction accuracy of the air flow rate may decrease dueto noise included in the rotation speed information, and the like.

Accordingly, it is conceivable that a pulsation state that is a state ofpulsation generated in the air flow rate is calculated using an outputvalue of a sensing unit in the air flow sensor instead of being acquiredfrom an external ECU, and the air flow rate is corrected using thispulsation state.

Then, for example, the output value when a change of the output valueswitches from increase to decrease is detected as an upper extremevalue, and the pulsation frequency is calculated on the basis of a timeinterval in which the output value becomes the upper extreme value.Alternatively, the output value when a change of the output valueswitches from decrease to increase is detected as a lower extreme value,and the pulsation frequency is calculated on the basis of the timeinterval at which the output value becomes the lower extreme value. Theair flow rate is corrected on the basis of the pulsation state includingthe pulsation frequency.

However, when the output value changes abruptly due to influence ofharmonics or sudden changes in the air flow rate, or the like, the upperextreme value or the lower extreme value may be erroneously detected. Inthis case, the correction accuracy of the air flow rate may deteriorate.

The present disclosure provides a measurement control device to improvethe correction accuracy of the air flow rate.

According to an aspect of the present disclosure, a measurement controldevice includes: a sensing unit that outputs a signal according to anair flow rate; a pulsation state calculation unit that calculates apulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate using the pulsationstate calculated by the pulsation state calculation unit. The pulsationstate calculation unit has: an upper extreme value determination unitthat, when the output value when a change mode of the output valueswitches from increase to decrease is referred to as an upper extremevalue, determines whether the output value has become the upper extremevalue; and a frequency calculation unit that calculates a pulsationfrequency of the pulsation generated in the air flow rate on a basis ofa time interval at which the output value becomes the upper extremevalue, and calculates the pulsation state including the pulsationfrequency. The upper extreme value determination unit, when the outputvalue remains to be more than a predetermined lower threshold during aperiod from a timing when the upper extreme value has previouslyappeared to a timing when the upper extreme value has presently appearedin a waveform representing a time change of the output value, negativelydetermines and cancels the upper extreme value that has presentlyappeared, and further updates the lower threshold on a basis of at leastone of the air flow rate specified on a basis of the output value, thepulsation frequency, or a pulsation amplitude specified on the basis ofthe output value.

With such a configuration, the lower threshold is updated on the basisof at least one of the air flow rate specified on the basis of theoutput value, the pulsation frequency, and the pulsation amplitudespecified on the basis of the output value, and thus false detection ofthe upper extreme value is reduced. Therefore, the correction accuracyof the air flow rate can be improved.

According to another aspect of the present disclosure, a measurementcontrol device includes: a sensing unit that outputs a signal accordingto an air flow rate; a pulsation state calculation unit that calculatesa pulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate using the pulsationstate calculated by the pulsation state calculation unit. The pulsationstate calculation unit has: an upper extreme value determination unitthat, when the output value when a change mode of the output valueswitches from increase to decrease is referred to as an upper extremevalue, determines whether the output value has become the upper extremevalue; and a frequency calculation unit that calculates a pulsationfrequency of the pulsation generated in the air flow rate on a basis ofa time interval at which the output value becomes the upper extremevalue, and calculates the pulsation state including the pulsationfrequency. The upper extreme value determination unit, when the outputvalue remains to be more than a predetermined lower threshold during aperiod from a timing when the upper extreme value has previouslyappeared to a timing when the upper extreme value has presently appearedin a waveform representing a time change of the output value, negativelydetermines and cancels the upper extreme value that has presentlyappeared, and further updates the lower threshold on a basis of areference value of the lower threshold that changes according to thepulsation state.

With such a configuration, the lower threshold is updated on the basisof the reference value of the lower threshold that changes according tothe pulsation state, and thus false detection of the upper extreme valueis reduced. Therefore, the correction accuracy of the air flow rate canbe improved.

According to another aspect of the present disclosure, a measurementcontrol device includes: a sensing unit that outputs a signal accordingto an air flow rate; a pulsation state calculation unit that calculatesa pulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate using the pulsationstate calculated by the pulsation state calculation unit. The pulsationstate calculation unit has: an upper extreme value determination unitthat, when the output value when a change mode of the output valueswitches from increase to decrease is referred to as an upper extremevalue, determines whether the output value has become the upper extremevalue; and a frequency calculation unit that calculates a pulsationfrequency of the pulsation generated in the air flow rate on a basis ofa time interval at which the output value becomes the upper extremevalue, and calculates the pulsation state including the pulsationfrequency. The upper extreme value determination unit, when the outputvalue remains to be more than a predetermined lower threshold during aperiod from a timing when the upper extreme value has previouslyappeared to a timing when the upper extreme value has presently appearedin a waveform representing a time change of the output value, negativelydetermines and cancels the upper extreme value that has presentlyappeared, and further updates the lower threshold by using the lowerthreshold used for determining the upper extreme value in a period frombefore a predetermined period to the timing when the upper extreme valuehas presently appeared.

With such a configuration, the lower threshold is updated by using thelower threshold used for determining the upper extreme value in theperiod from before the predetermined period to the timing when the upperextreme value has presently appeared, so that the false detection of theupper extreme value is reduced. Therefore, the correction accuracy ofthe air flow rate can be improved.

According to another aspect of the present disclosure, a measurementcontrol device includes: a sensing unit that outputs a signal accordingto an air flow rate; a pulsation state calculation unit that calculatesa pulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate using the pulsationstate calculated by the pulsation state calculation unit. The pulsationstate calculation unit has a lower extreme value determination unitthat, when the output value when a change mode of the output valueswitches from decrease to increase is referred to as a lower extremevalue, determines whether the output value has become the lower extremevalue. The lower extreme value determination unit, when the output valueremains to be less than a predetermined upper threshold during a periodfrom a timing when the lower extreme value has previously appeared to atiming when the lower extreme value has presently appeared in a waveformrepresenting a time change of the output value, negatively determinesand cancels the lower extreme value that has presently appeared, andfurther updates the upper threshold on a basis of at least one of theair flow rate specified on a basis of the output value, a pulsationfrequency specified on the basis of the output value, or a pulsationamplitude specified on the basis of the output value.

With such a configuration, the upper threshold is updated on the basisof at least one of the air flow rate specified on the basis of theoutput value, the pulsation frequency specified on the basis of theoutput value, or the pulsation amplitude specified on the basis of theoutput value, and thus false detection of the lower extreme value isreduced. Therefore, the correction accuracy of the air flow rate can beimproved.

According to another aspect of the present disclosure, a measurementcontrol device includes: a sensing unit that outputs a signal accordingto an air flow rate; a pulsation state calculation unit that calculatesa pulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate using the pulsationstate calculated by the pulsation state calculation unit. The pulsationstate calculation unit has: a lower extreme value determination unitthat, when the output value when a change mode of the output valueswitches from decrease to increase is referred to as a lower extremevalue, determines whether the output value has become the lower extremevalue; and a frequency calculation unit that calculates a pulsationfrequency of the pulsation generated in the air flow rate on a basis ofa time interval at which the output value becomes the lower extremevalue, and calculates the pulsation state including the pulsationfrequency. The lower extreme value determination unit, when the outputvalue remains to be less than a predetermined upper threshold during aperiod from a timing when the lower extreme value has previouslyappeared to a timing when the lower extreme value has presently appearedin a waveform representing a time change of the output value, negativelydetermines and cancels the lower extreme value that has presentlyappeared, and further updates the upper threshold on a basis of areference value of the upper threshold that changes according to thepulsation state.

With such a configuration, the upper threshold is updated on the basisof the reference value of the upper threshold that changes according tothe pulsation state, and thus erroneous detection of the lower extremevalue is reduced. Therefore, the correction accuracy of the air flowrate can be improved.

According to another aspect of the present disclosure, a measurementcontrol device includes: a sensing unit that outputs a signal accordingto an air flow rate; a pulsation state calculation unit that calculatesa pulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit that corrects the air flow rate using the pulsationstate calculated by the pulsation state calculation unit. The pulsationstate calculation unit has: a lower extreme value determination unitthat, when the output value when a change mode of the output valueswitches from decrease to increase is referred to as a lower extremevalue, determines whether the output value has become the lower extremevalue; and a frequency calculation unit that calculates a pulsationfrequency of the pulsation generated in the air flow rate on a basis ofa time interval at which the output value becomes the lower extremevalue, and calculates the pulsation state including the pulsationfrequency. The lower extreme value determination unit, when the outputvalue remains to be less than a predetermined upper threshold during aperiod from a timing when the lower extreme value has previouslyappeared to a timing when the lower extreme value has presently appearedin a waveform representing a time change of the output value, negativelydetermines and cancels the lower extreme value that has presentlyappeared, and further updates the upper threshold by using the upperthreshold used for determining the lower extreme value in a period frombefore a predetermined period to the timing when the lower extreme valuehas presently appeared.

With such a configuration, the upper threshold is updated by using theupper threshold used for determining the lower extreme value in theperiod from before the predetermined period to the timing when the lowerextreme value has presently appeared, and thus false detection of thelower extreme value is reduced. Therefore, the correction accuracy ofthe air flow rate can be improved.

Reference numerals attached to respective components and the likeindicate an example of a correspondence relationship between thecomponents and the like and specific components and the like describedin embodiments described later.

Embodiments of the present disclosure will be described hereafterreferring to drawings. In the embodiments, a part that corresponds to amatter described in a preceding embodiment may be assigned with the samereference numeral, and redundant explanation for the part may beomitted. When only a part of a configuration is described in anembodiment, another preceding embodiment may be applied to the otherparts of the configuration. The parts may be combined even if it is notexplicitly described that the parts can be combined. The embodiments maybe partially combined even if it is not explicitly described that theembodiments can be combined, provided there is no harm in thecombination.

(First Embodiment)

An air flow meter 10 as a measurement control device illustrated inFIGS. 1 and 2 is included in a combustion system having an internalcombustion engine such as a gasoline engine. This combustion system isinstalled in a vehicle. As illustrated in FIG. 3, the air flow meter 10is provided in an intake passage 12 for supplying intake air to aninternal combustion engine in the combustion system, and physicalquantities such as a flow rate, temperature, humidity, and pressure of afluid including gas such as intake air flowing through the intakepassage 12 are measured. In this case, the air flow meter 10 correspondsto a flow rate measurement device.

The air flow meter 10 is attached to an intake pipe 12 a such as anintake duct forming the intake passage 12. The intake pipe 12 a has anair flow insertion hole 12 b as a through hole penetrating an outerperipheral portion thereof. An annular pipe flange 12 c is attached tothe air flow insertion hole 12 b, and this pipe flange 12 c is includedin the intake pipe 12 a. The air flow meter 10 is inserted into the pipeflange 12 c and the air flow insertion hole 12 b and has thereby enteredthe intake passage 12, and is fixed to the intake pipe 12 a and the pipeflange 12 c in this state.

In the present embodiment, a width direction X, a height direction Y,and a depth direction Z of the air flow meter 10 are orthogonal to eachother. The air flow meter 10 extends in the height direction Y, and theintake passage 12 extends in the depth direction Z. The air flow meter10 has an entering portion 10 a that has entered the intake passage 12and a protruding portion 10 b that protrudes from the pipe flange 12 cwithout entering the intake passage 12, and the entering portion 10 aand the protruding portion 10 b are aligned in the height direction Y.The air flow meter 10 has end surfaces 10 c and 10 d in which oneincluded in the entering portion 10 a will be referred to as an air flowdistal end surface 10 c, and the other included in the protrudingportion 10 b will be referred to as an air flow base end surface 10 d.In this case, the air flow distal end surface 10 c and the air flow baseend surface 10 d are aligned in the height direction Y. The air flowdistal end surface 10 c and the air flow base end surface 10 d areorthogonal to the height direction Y. The distal end surface of the pipeflange 12 c is also orthogonal to the height direction Y.

As illustrated in FIGS. 1 to 3, the air flow meter 10 has a housing 21and a sensing unit 22 for detecting a flow rate of intake air. Thesensing unit 22 is provided in an internal space 24 a of a housing body24. The housing 21 is formed by, for example, a resin material or thelike. By attaching the housing 21 of the air flow meter 10 to the intakepipe 12 a, the sensing unit 22 is in a state where it can come intocontact with the intake air flowing through the intake passage 12. Thehousing 21 has a housing body 24, a ring holding portion 25, a flangeportion 27, and a connector portion 28. As illustrated in FIG. 3, anO-ring 26 is attached to the ring holding portion 25.

As illustrated in FIGS. 1 to 3, the housing body 24 has an appearanceformed in a columnar shape extending in the height direction Y as awhole. The housing 21 is in a state where the ring holding portion 25,the flange portion 27, and the connector portion 28 are integrallyprovided with the housing body 24. The ring holding portion 25 isincluded in the entering portion 10 a, and the flange portion 27 and theconnector portion 28 are included in the protruding portion 10 b.

The ring holding portion 25 is provided inside the pipe flange 12 c andholds the O-ring 26 so that the O-ring is not displaced in the heightdirection Y. The O-ring 26 is a sealing member that seals the intakepassage 12 inside the pipe flange 12 c, and is in close contact withboth an outer peripheral surface of the ring holding portion 25 and aninner peripheral surface of the pipe flange 12 c. The flange portion 27is formed with a fixing hole such as a screw hole for fixing a fixturesuch as a screw for fixing the air flow meter 10 to the intake pipe 12a. The connector portion 28 is a protective unit that protects aconnector terminal electrically connected to the sensing unit 22.

As illustrated in FIG. 3, the housing body 24 forms a bypass passage 30through which a part of the intake air flowing through the intakepassage 12 flows. The bypass passage 30 is arranged in the enteringportion 10 a of the air flow meter 10. The bypass passage 30 has apassage path 31 and a measurement path 32, and the passage path 31 andthe measurement path 32 are formed by the internal space 24 a of thehousing body 24. The intake passage 12 can also be referred to as a mainpassage, and the bypass passage 30 can also be referred to as a subpassage.

The passage path 31 penetrates the housing body 24 in the depthdirection Z. The passage path 31 has an inflow port 33 that is anupstream end thereof and an outflow port 34 that is a downstream endthereof. The inflow port 33 and the outflow port 34 are arranged in thedepth direction Z, and the depth direction Z corresponds to anarrangement direction. The measurement path 32 is a branch passagebranched from an intermediate portion of the passage path 31, and thesensing unit 22 is provided in the measurement path 32. The measurementpath 32 has a measurement inlet 35 that is an upstream end thereof and ameasurement outlet 36 that is a downstream end thereof. The portionwhere the measurement path 32 branches from the passage path 31 is aboundary portion between the passage path 31 and the measurement path32, and the measurement inlet 35 is included in this boundary portion.

The sensing unit 22 has a circuit board and a detection element mountedon the circuit board, and is a chip-type flow sensor. The detectionelement has a heater unit such as a heat generation resistor and atemperature detection unit that detects a temperature of air heated bythe heater unit. The sensing unit 22 outputs an output signal from thetemperature detection unit according to a change in temperature due toheat generation of the heater unit in the detection element. The sensingunit 22 can also be referred to as a flow rate detecting unit.

The air flow meter 10 has a sensor sub-assembly including the sensingunit 22, and this sensor sub-assembly will be referred to as a sensor SA40. The sensor SA 40 is housed in the housing body 24. In addition tothe sensing unit 22, the sensor SA 40 has a circuit chip 41 electricallyconnected to the sensing unit 22, and a mold unit 42 that protects thesensing unit 22 and the circuit chip 41. The circuit chip 41 has adigital circuit that performs various processes, and is a rectangularparallelepiped chip component. In the sensor SA 40, the sensing unit 22and the circuit chip 41 are supported by a lead frame, and the circuitchip 41 is electrically connected to the sensing unit 22 and the leadframe via a bonding wire or the like.

The mold unit 42 is a mold resin such as a polymer resin molded bymolding, and has higher insulating properties than the lead frame andthe bonding wire. The mold unit 42 protects the circuit chip 41 and thesensing unit 22 in a state where the circuit chip 41, the bonding wire,and the like are sealed. In the sensor SA 40, the sensing unit 22 andthe circuit chip 41 are mounted in one package by the mold unit 42. Thesensor SA 40 can also be referred to as a detection unit or a sensorunit.

The sensing unit 22 outputs an output signal according to the air flowrate in the measurement path 32 to the circuit chip 41, and the circuitchip 41 calculates the flow rate using the output signal of the sensingunit 22. The calculation result of the circuit chip 41 is the flow rateof air measured by the air flow meter 10. The inflow port 33 and theoutflow port 34 of the air flow meter 10 are arranged at a centerposition of the intake passage 12 in the height direction Y. The intakeair flowing through the central position of the intake passage 12 in theheight direction Y flows along the depth direction Z. The direction inwhich the intake air flows in the intake passage 12 and the direction inwhich the intake air flows in the passage path 31 are substantially thesame. The sensing unit 22 is not limited to a thermal type flow sensor,and may be an ultrasonic type flow sensor, a Karman vortex type flowsensor, or the like.

As illustrated in FIG. 4, an outer peripheral surface of the housingbody 24 included in the housing 21 has an upstream outer surface 24 b, adownstream outer surface 24 c, and an intermediate outer surface 24 d.On the outer peripheral surface of the housing body 24, the upstreamouter surface 24 b faces an upstream side of the intake passage 12, andthe downstream outer surface 24 c faces a downstream side of the intakepassage 12. The pair of intermediate outer surfaces 24 d face oppositesides to each other in the width direction X and are flat surfacesextending in the depth direction Z. The upstream outer surface 24 b isan inclined surface inclined with respect to the intermediate outersurfaces 24 d. In this case, the upstream outer surface 24 b is aninclined surface curved so as to gradually reduce a width dimension ofthe housing body 24 toward the upstream side in the intake passage 12 inthe width direction X.

The intermediate outer surface 24 d is provided between the upstreamouter surface 24 b and the downstream outer surface 24 c in the depthdirection Z. In this case, the upstream outer surface 24 b and theintermediate outer surface 24 d are arranged in the depth direction Z,and a surface boundary portion 24 e, which is a boundary between theupstream outer surface 24 b and the intermediate outer surface 24 d,extends in the height direction Y. The upstream outer surface 24 b andthe downstream outer surface 24 c are end surfaces facing opposite toeach other in the depth direction Z.

As illustrated in FIG. 3, the inflow port 33 is provided on the upstreamouter surface 24 b, and the outflow port 34 is provided on thedownstream outer surface 24 c. In this case, the inflow port 33 and theoutflow port 34 are open in opposite directions. As illustrated in FIG.4, the measurement outlet 36 is provided on both the upstream outersurface 24 b and the intermediate outer surface 24 d by arranging themeasurement outlet 36 at a position over the surface boundary portion 24e in the depth direction Z. In the measurement outlet 36, a portionarranged on the upstream outer surface 24 b is open to face a directioninclined toward the inflow port 33 with respect to the width directionX, and a portion arranged on the intermediate outer surface 24 d is openin the width direction X. In this case, the measurement outlet 36 is notopen toward the outflow port 34. That is, the measurement outlet 36 isnot open toward the downstream side in the intake passage 12.

The measurement outlet 36 has a vertically long flat shape extendingalong the surface boundary portion 24 e. The measurement outlet 36 isarranged at a position closer to the intermediate outer surface 24 dwith reference to the surface boundary portion 24 e in the depthdirection Z. In the measurement outlet 36, the area of a portionarranged on the intermediate outer surface 24 d is larger than the areaof a portion arranged on the upstream outer surface 24 b. In this case,in the depth direction Z, a separation distance between a downstream end36 b of the measurement outlet 36 and the surface boundary portion 24 eis larger than a separation distance between an upstream end 36 a of themeasurement outlet 36 and the surface boundary portion 24 e.

An inner peripheral surface of the measurement path 32 has formationsurfaces 38 a to 38 c forming the measurement outlet 36. A through holeforming the measurement outlet 36 is provided in an outer peripheralportion of the housing body 24, and the formation surfaces 38 a to 38 care included in an inner peripheral surface of the through hole. Amongthe formation surfaces 38 a to 38 c, the upstream formation surface 38 aforms the upstream end 36 a of the measurement outlet 36, and thedownstream formation surface 38 b forms the downstream end 36 b of themeasurement outlet 36. The connection formation surfaces 38 c connectthe upstream formation surface 38 a and the downstream formation surface38 b, and provided in a pair sandwiching the formation surfaces 38 a and38 b.

The upstream formation surface 38 a is orthogonal to the depth directionZ and extends in the width direction X from the upstream end 36 a of themeasurement outlet 36 toward the inside of the housing body 24. Thedownstream formation surface 38 b is inclined with respect to the depthdirection Z, and is an inclined surface extending straight from thedownstream end 36 b of the measurement outlet 36 into the housing body24 toward the upstream outer surface 24 b.

The flow of intake air generated on an outer peripheral side of thehousing body 24 in the intake passage 12 will be briefly described. Inair flowing toward the downstream side of the intake passage 12, airthat has reached the upstream outer surface 24 b of the housing body 24travels along the upstream outer surface 24 b, which is an inclinedsurface, to thereby gradually change in its direction to reach themeasurement outlet 36. In this manner, the direction of the air issmoothly changed by the upstream outer surface 24 b, and thus it isdifficult for the air to separate in the vicinity of the measurementoutlet 36. Thus, it is easy for the air flowing through the measurementpath 32 to flow out from the measurement outlet 36, and a flow velocityin the measurement path 32 tends to be stable.

The air flowing through the measurement path 32 and flowing out from themeasurement outlet 36 to the intake passage 12 flows along thedownstream formation surface 38 b, which is an inclined surface, so thatthe air easily flows toward the downstream side in the intake passage12. In this case, when the air flowing out from the measurement outlet36 along the downstream formation surface 38 b joins the intake airflowing through the intake passage 12, turbulence such as a vortex isless likely to occur, so that the flow velocity of the inside of themeasurement path 32 tends to be stable.

As illustrated in FIG. 3, the measurement path 32 has a folded shapethat is folded back between the measurement inlet 35 and the measurementoutlet 36. The measurement path 32 includes a branch path 32 a branchedfrom the passage path 31, a guide path 32 b that guides air flowing fromthe branch path 32 a toward the sensing unit 22, a detection path 32 cprovided with the sensing unit 22, and a discharge path 32 d thatdischarges air from the measurement outlet 36. In the measurement path32, the branch path 32 a, the guide path 32 b, the detection path 32 c,and the discharge path 32 d are arranged in this order from the upstreamside.

The detection path 32 c is in parallel to the passage path 31 byextending in the depth direction Z, and is provided at a positionseparated from the passage path 31 toward the protruding portion 10 b.The branch path 32 a, the guide path 32 b, and the discharge path 32 dare provided between the detection path 32 c and the passage path 31.The guide path 32 b and the discharge path 32 d are parallel to eachother because they extend in the height direction Y from the detectionpath 32 c toward the passage path 31. The branch path 32 a extends fromthe measurement inlet 35 toward the detection path 32 c and thedownstream outer surface 24 c so as to be inclined with respect to thedepth direction Z, and is a straight flow path. The discharge path 32 dis provided between the inflow port 33 and the guide path 32 b in thedepth direction Z, and extends from the measurement outlet 36 toward thedetection path 32 c.

As illustrated in FIG. 5, the sensor SA 40 is arranged at a positionwhere the sensing unit 22 has entered the detection path 32 c. Thesensing unit 22 is arranged between the pair of intermediate outersurfaces 24 d in the width direction X, and extends in the depthdirection Z and the height direction Y. The sensing unit 22 is in astate of partitioning the detection path 32 c in the width direction X.

The housing 21 has a detection narrow portion 37 that gradually narrowsthe detection path 32 c toward the sensing unit 22 in the depthdirection Z. The detection narrow portion 37 gradually reduces across-sectional area of the detection path 32 c from the downstreamouter surface 24 c toward the sensing unit 22 in the detection path 32c. The detection narrow portion 37 gradually reduces the cross-sectionalarea of the detection path 32 c from the upstream outer surface 24 btoward the sensing unit 22 in the detection path 32 c. In the detectionpath 32 c, the cross-sectional area is defined as a cross-sectional areain a direction orthogonal to the depth direction Z. When air is flowingin the forward direction toward the sensing unit 22 in the detectionpath 32 c, the detection narrow portion 37 can adjust the direction ofair flow by gradually reducing the detection path 32 c.

The detection narrow portion 37 is provided at a position facing thesensing unit 22 on an inner peripheral surface of the detection path 32c. The detection narrow portion 37 protrudes from an inner peripheralsurface of the housing body 24 toward the sensing unit 22, and a depthdimension D1 of the detection narrow portion 37 in the depth direction Zis larger than a depth dimension D2 of the sensing unit 22 in the depthdirection Z. In a region where the sensing unit 22 exists in the heightdirection Y, a depth dimension D3 of the mold unit 42 in the depthdirection Z is larger than the depth dimension D1 of the detectionnarrow portion 37.

The detection narrow portion 37 has a tapered shape in the widthdirection X. Specifically, a base end portion of the detection narrowportion 37 protruding in the width direction X from an inner wall of thehousing body 24 is the widest portion, and a distal end portion thereofis the narrowest portion. A width dimension of the base end portion ofthe detection narrow portion 37 is defined as the above-mentioned depthdimension D1. The detection narrow portion 37 has a curved surface thatbulges toward the sensing unit 22. The detection narrow portion 37 mayhave a tapered shape that bulges toward the sensing unit 22.

In the inner peripheral surface of the detection path 32 c, when asurface on the air flow distal end surface 10 c side is referred to as abottom surface, and a surface on the air flow base end surface 10 d sideis referred to as a ceiling surface, the bottom surface of the detectionpath 32 c is formed by the housing body 24, and meanwhile the ceilingsurface is formed by the sensor SA 40. The detection narrow portion 37extends from the bottom surface of the detection path 32 c toward theceiling surface. An outer peripheral surface of the detection narrowportion 37 extends straight in the height direction Y.

The detection path 32 c has a configuration in which a separationdistance between the mold unit 42 and the detection narrow portion 37gradually decreases while approaching the sensing unit 22 in the depthdirection Z. In this configuration, when the intake air flowing from theguide path 32 b to the detection path 32 c passes between the mold unit42 and the detection narrow portion 37, the flow velocity of the intakeair tends to increase as the air approaches the sensing unit 22. In thiscase, since the intake air is given to the sensing unit 22 at anappropriate flow rate, the output of the sensing unit 22 tends to bestable, and detection accuracy can be improved.

In the intake passage 12, when a pulsation such as an intake pulsationoccurs in the flow of intake air due to the operating state of theengine or the like, in addition to a forward flow from the upstreamside, a backflow that flows in an opposite direction of the forward flowmay occur from the downstream side accompanying this pulsation. In theintake passage 12, the inflow port 33 of the passage path 31 is opentoward the upstream side of the intake passage 12, and the forward flowcan easily flow into the inflow port 33. The outflow port 34 of thepassage path 31 is open toward the downstream side of the intake passage12, and the backflow easily flows into the outflow port 34. Moreover, inthe intake passage 12, the measurement outlet 36 of the measurement path32 is not open toward the downstream side of the intake passage 12, andthe backflow is less likely to flow into the measurement outlet 36.

Unlike the present embodiment, for example, in a configuration in whicha part of the outer peripheral surface is a stepped surface facing thedownstream side in the housing body 24, and the measurement outlet 36 isformed on this stepped surface, it is conceivable that turbulence suchas vortex is likely to occur in the air passing through the steppedsurface in the intake passage 12. On the other hand, in the presentembodiment, since the measurement outlet 36 is not formed on the steppedsurface, the turbulence of the air flow is less likely to occur aroundthe measurement outlet 36, and a case where easiness of the backflow toenter the measurement outlet 36 fluctuates is less likely to occur. Asdescribed above, since unstable backflow is unlikely to occur in themeasurement path 32, stable pulsation measurement can be achieved in theair flow meter 10.

As illustrated in FIG. 6, the air flow meter 10 has a processing unit 45that processes an output signal of the sensing unit 22. The processingunit 45 is provided on the circuit chip 41 and is electrically connectedto the ECU (Electronic Control Unit) 46. The ECU 46 is an engine controldevice having a function of controlling the engine on the basis of ameasurement signal from the air flow meter 10, and the like. Themeasurement signal from the air flow meter 10 is an electric signalindicating the air flow rate corrected by a pulsation error correctionunit 61 described later. One-way communication is possible between theprocessing unit 45 and the ECU 46, and while the processing unit 45inputs a signal to the ECU 46, the ECU 46 does not input a signal to theprocessing unit 45. The ECU 46 is provided independently of theprocessing unit 45 and the air flow meter 10, and corresponds to anexternal device.

The ECU 46 is electrically connected to an engine sensor such as a crankangle sensor and a cam angle sensor. The ECU 46 acquires engineparameters such as a rotation angle, a rotation speed, and rotationnumber of the engine using the detection signal of the engine sensor,and controls the engine using these engine parameters. The pulsationgenerated in the intake air in the intake passage 12 correlates with theengine parameters. However, the ECU 46 of the present embodiment doesnot output the engine parameters to the processing unit 45, and theprocessing unit 45 does not use the engine parameter when performingprocessing such as correction for the output signal of the sensing unit22.

The sensing unit 22 outputs an output signal corresponding to the airflow rate flowing through the measurement path 32 to the processing unit45. This output signal is an electric signal, a sensor signal, and adetection signal output from the sensing unit 22, and the output valuecorresponding to the value of the air flow rate is included in thisoutput signal. The sensing unit 22 can detect the air flow rate for boththe air flowing forward in the measurement path 32 from the measurementinlet 35 to the measurement outlet 36 and the air flowing in the reversedirection from the measurement outlet 36 toward the measurement inlet35. The output value of the sensing unit 22 becomes a positive valuewhen the air is flowing in the forward direction in the measurement path32, and becomes a negative value when the air is flowing in the reversedirection therein.

When a pulsation occurs in the air flow in the intake passage 12, thesensing unit 22 is affected by the pulsation, and an error with respectto a true air flow rate occurs in the output value. In particular, inthe sensing unit 22, when the throttle valve is operated to the fullyopen side, a pulsation amplitude and a pulsation rate tend to increase.In the following, this error by pulsation is also referred to as apulsation error Err. The true air flow rate is an air flow rate that isnot affected by pulsation. The pulsation rate is a value obtained bydividing the pulsation amplitude by an average value.

The processing unit 45 detects an air flow rate on the basis of anoutput value of the sensing unit 22, and outputs the detected air flowrate to the ECU 46. The processing unit 45 has a drive circuit 49 thatdrives the heater unit of the sensing unit 22, a correction circuit 50that corrects the output value of the sensing unit 22, and an outputcircuit 62 that outputs a correction result of the correction circuit 50to the ECU 46. The drive circuit 49 supplies electric power used fordriving the heater unit and the like to the sensing unit 22, in additionto drive control of the heater unit. The drive circuit 49 performspreprocessing such as amplifying an output signal of the sensing unit 22at a stage before the correction circuit 50 performs a correctionprocess.

The processing unit 45 has an arithmetic processing device such as a CPUand a storage device for storing programs and data. For example, theprocessing unit 45 is achieved by a microcomputer having a storagedevice that can be read by a computer. The processing unit 45 calculatesan air flow rate by performing various calculations by executing aprogram stored in the storage device by the arithmetic processingdevice, and outputs the calculated air flow rate to the ECU 46.

A storage device is a non-transitional tangible storage medium thatstores computer-readable programs and data non-temporarily. The storagemedium is achieved by a semiconductor memory or the like. This storagedevice can also be rephrased as a storage medium. The processing unit 45may include a volatile memory for temporarily storing data.

The processing unit 45 has a function of correcting an output value inwhich the pulsation error Err has occurred. In other words, theprocessing unit 45 corrects the air flow rate of the output signal so asto approach the true air flow rate. Therefore, the processing unit 45outputs the air flow rate corrected for the pulsation error Err to theECU 46 as a measurement signal. The measurement signal includes ameasurement value that is a correction result of the output value.

The processing unit 45 operates as a plurality of functional blocks byexecuting a program. The drive circuit 49, the correction circuit 50,and the output circuit 62 are all functional blocks. As illustrated inFIG. 7, the correction circuit 50 has an A/D conversion unit 51, asampling unit 52, a variation adjustment unit 53, a conversion table 54,and the like as functional blocks.

The A/D conversion unit 51 A/D-converts an output value input from thesensing unit 22 to the correction circuit 50 via the drive circuit 49.The sampling unit 52 samples the A/D-converted output value at apredetermined sampling interval Δt, and acquires a sampling value atevery timing. These sampling values are included in the output value.The variation adjustment unit 53 adjusts variations of the output valueof the sensing unit 22 so that measurement values do not vary due toindividual differences of the air flow meter 10, such as an individualdifference of the sensing unit 22. Specifically, the variationadjustment unit 53 reduces individual variations in a flow rate outputcharacteristic indicating the relationship between the output value andthe actual air flow rate and a temperature characteristic indicating therelationship between the flow rate output characteristic and thetemperature.

The conversion table 54 converts the sampling value acquired by thesampling unit 52 into an air flow rate. In the present embodiment, thevalue converted in the conversion table 54 may be referred to as asampling value or an output value instead of an air flow rate. Theconversion table 54 is a conversion table that uses the flow rate outputcharacteristic.

Further, in addition to the components described above as functionalblocks, the correction circuit 50 includes an upper extreme valuedetermination unit 56, an average air amount calculation unit 57, apulsation amplitude calculation unit 58, a frequency calculation unit59, a pulsation error calculation unit 60, a correction amountcalculation unit 60 a, and a pulsation error correction unit 61.

The upper extreme value determination unit 56 determines whether or notthe sampling value converted in the conversion table 54 is an upperextreme value Ea. The upper extreme value Ea is a sampling value at atiming when the output value switches from increase to decrease. Theupper extreme value determination unit 56 acquires a timing when thesampling value has become the upper extreme value Ea as an upper extremetiming ta, and causes the timing to be stored in the storage device ofthe processing unit 45. The upper extreme value determination unit 56outputs information including the upper extreme timing ta as timinginformation indicating a pulsation cycle to the average air amountcalculation unit 57, the pulsation amplitude calculation unit 58, andthe frequency calculation unit 59. In FIG. 7, an output of informationrelated to the output value of the sensing unit 22 is illustrated by asolid line, and an output of the timing information is illustrated by abroken line.

The frequency calculation unit 59 uses the timing information from theupper extreme value determination unit 56 to calculate the interval atwhich the sampling value becomes the upper extreme value Ea as an upperextreme interval Wa, and uses this upper extreme interval Wa tocalculate the pulsation frequency F. For example, as illustrated in FIG.8, for a case where the sampling value becomes the upper extreme valueEa and then the sampling value becomes the next extreme value Ea, theprevious extreme value Ea will be referred to as a first extreme valueEa1, the next extreme value Ea will be referred to as a second extremevalue Ea2. In this case, the frequency calculation unit 59 uses a firstupper extreme timing ta1 at which the sampling value becomes the firstupper extreme value Ea1 and a second upper extreme timing ta2 at whichthe sampling value becomes the second upper extreme value Ea2, andcalculates the upper extreme interval Wa, which is an interval betweenthe upper extreme timing ta1 and ta2. For example, the pulsationfrequency F is calculated using the relationship F [Hz]=1/Wa[s]. Theupper extreme interval Wa corresponds to the time interval.

For the period from the first upper extreme timing ta1 to the secondupper extreme timing ta2, a maximum pulsation value Gmax, which is amaximum value of the air flow rate when the air is pulsating, is thelarger one of the first upper extreme value Ea1 and the second upperextreme values Ea2. When these upper extreme values Ea1 and Ea2 are thesame value, that value becomes the maximum pulsation value Gmax. Theaverage value of the first upper extreme value Ea1 and the second upperextreme value Ea2 may be the maximum pulsation value Gmax.

Between the first upper extreme value Ea1 and the second upper extremevalue Ea2, there is a lower extreme value Eb, which is a sampling valueat a timing when the output value switches from decrease to increase.There is only one lower extreme value Eb between the first upper extremetiming ta1 and the second upper extreme timing ta2, and thus this lowerextreme value Eb becomes a minimum pulsation value Gmin. FIG. 10illustrates the maximum pulsation value Gmax, the minimum pulsationvalue Gmin, and an average air amount Gave with respect to the air flowrate.

The frequency calculation unit 59 has a frequency limiting function thatlimits a change amount in the pulsation frequency F to be equal to orless than a predetermined maximum frequency change amount.

The frequency calculation unit 59 has an operation unit 59 a. Theoperation unit 59 a is for setting whether to enable or disable afrequency limiting function of the frequency calculation unit 59. Theoperation unit 59 a is formed by an on-off switch. The operation unit 59a outputs a signal according to the user's operation to the frequencycalculation unit 59.

The frequency calculation unit 59 switches enabling or disabling of thefrequency limiting function according to the signal input from theoperation unit 59 a.

The average air amount calculation unit 57 calculates an average airamount Gave, which is the average value of the air flow rate, by usingsampling values converted by the conversion table 54 and the timinginformation from the upper extreme value determination unit 56. Theaverage air amount calculation unit 57 sets a target period forcalculating the average air amount Gave as a measurement period using adetermination result of the upper extreme value determination unit 56,and calculates the average air amount Gave for this measurement period.For example, in FIG. 8, when the period from the first upper extremetiming ta1 to the second upper extreme timing ta2 is set as themeasurement period, the average air amount Gave is calculated for thismeasurement period.

The average air amount calculation unit 57 calculates the average airamount Gave using, for example, an integrated average. Here, as anexample, calculation of the average air amount Gave using the waveformillustrated in FIG. 9 will be described. In this example, themeasurement period is from timing t1 to timing tn, an air flow rate attiming t1 is G1, and an air flow rate at timing tn is Gn. The averageair amount calculation unit 57 calculates the average air amount Gave byusing Expression 1 described in FIG. 9. In this case, it is possible tocalculate the average air amount Gave in which the influence of theminimum pulsation value Gmin, which has relatively low detectionaccuracy, is reduced when the number of samplings is large rather thanwhen the number of samplings is small.

In the measurement path 32, if the actual air flow rate is sufficientlylarge, a streamline is less likely to fluctuate when air travels towardthe measurement outlet 36, and it is conceivable that the travelingdirection and flow rate of the air passing through the sensing unit 22tend to be stable. Thus, detection accuracy of the sensing unit 22 tendsto be high because the actual air flow rate is sufficiently large. Onthe other hand, as the actual air flow rate decreases, the travelingdirection and flow rate of the air tends to be unstable. For example,when the actual air flow rate in the measurement path 32 is the smallestin the range in which no backflow occurs, it is conceivable that thetraveling direction and flow rate of the air are not stable because theair meanders while traveling toward the measurement outlet 36, or thelike. Therefore, as the actual air flow rate decreases, the detectionaccuracy of the sensing unit 22 tends to decrease. Therefore, thedetection accuracy of the sensing unit 22 is relatively low for theminimum pulsation value Gmin among the output values.

The pulsation amplitude calculation unit 58 calculates a pulsationamplitude Pa, which is the magnitude of the pulsation generated by theair flow rate, using the sampling value converted by the conversiontable 54 and the timing information from the upper extreme valuedetermination unit 56. The pulsation amplitude calculation unit 58targets the measurement period for calculation, and as illustrated inFIG. 10, calculates the pulsation amplitude Pa of the air flow rate bytaking a difference between the maximum pulsation value Gmax and theaverage air amount Gave. That is, the pulsation amplitude calculationunit 58 obtains a half amplitude of the air flow rate instead of thetotal amplitude of the air flow rate. This is to reduce the influence ofthe minimum pulsation value Gmin, which has relatively low detectionaccuracy as described above. The pulsation amplitude calculation unit 58may calculate the total amplitude, which is a difference between themaximum pulsation value Gmax and the minimum pulsation value, as thepulsation amplitude.

Regarding the output value of the sensing unit 22, the upper extremevalue Ea, the pulsation frequency F, the pulsation amplitude Pa, and theaverage air amount Gave indicate a pulsation state that is a state ofpulsation, and correspond to the pulsation parameters. In this case, theupper extreme value determination unit 56, the average air amountcalculation unit 57, the pulsation amplitude calculation unit 58, andthe frequency calculation unit 59 correspond to a pulsation statecalculation unit for calculating the pulsation state.

The pulsation error calculation unit 60 calculates the pulsation errorErr correlated with the pulsation amplitude Pa for the air flow rate.The pulsation error calculation unit 60 predicts the pulsation error Errof the air flow rate by using, for example, a map in which the pulsationamplitude Pa and the pulsation error Err are associated with each other,or the like. That is, when the pulsation amplitude calculation unit 58obtains the pulsation amplitude Pa, the pulsation error calculation unit60 extracts the pulsation error Err that correlates with the obtainedpulsation amplitude Pa from the map. It can be said that the pulsationerror calculation unit 60 acquires the pulsation error Err thatcorrelates with the pulsation amplitude Pa for the measurement period asa target.

As described above, the air flow meter 10 is attached to the intake pipe12 a forming the intake passage 12. Thus, in the air flow meter 10, dueto influence of a shape of the intake pipe 12 a, or the like, not onlythe pulsation error Err increases as the pulsation amplitude Paincreases, but also the pulsation error Err can decrease as thepulsation amplitude Pa increases. Thus, there may be cases where, in theair flow meter 10, the relationship between the pulsation amplitude Paand the pulsation error Err cannot be expressed by a function.Therefore, the air flow meter 10 is preferable because the accuratepulsation error Err can be predicted by using the map as describedabove. The map may be associated with a plurality of pulsationamplitudes Pa and a correction amount Q correlated with each pulsationamplitude Pa.

However, there may be cases where, in the air flow meter 10, therelationship between the pulsation amplitude Pa and the pulsation errorErr by a function can be expressed in a case where the sensing unit 22is directly arranged in the main air passage, and the like. In thiscase, the air flow meter 10 may use this function to calculate thepulsation error Err. The air flow meter 10 does not need to have a mapby calculating the pulsation error Err using the function, and thus thecapacity of the storage device can be reduced. This point similarlyapplies to the following embodiments. That is, in the followingembodiment, the pulsation error Err may be obtained by using a functioninstead of the map.

The pulsation error Err is the difference between an uncorrected airflow rate obtained by the output value and the true air flow rate. Thatis, the pulsation error Err corresponds to the difference between theair flow rate whose output value is converted by the conversion table 54and the true air flow rate. Thus, the correction amount Q for bringingthe air amount before correction close to the true air flow rate can beobtained if the pulsation error Err is known.

As illustrated in FIG. 7, to the pulsation error calculation unit 60,the average air amount Gave calculated by the average air amountcalculation unit 57, the pulsation amplitude Pa calculated by thepulsation amplitude calculation unit 58, and the calculated pulsationfrequency F calculated by the frequency calculation unit 59 are input.The pulsation error calculation unit 60 calculates the pulsation errorErr using the average air amount Gave, the pulsation amplitude Pa, andthe pulsation frequency F.

When pulsation occurs in the air flow, as the average air amount Gaveincreases, the pulsation amplitude Pa tends to increase. When thepulsation amplitude Pa and the pulsation error Err are almost in aproportional relationship in the pulsation characteristics illustratingthe relationship between the pulsation amplitude Pa and the pulsationerror Err, an approximate line for the pulsation characteristics can beillustrated by a straight line as illustrated in FIG. 11.

Err=Ann×Pa+Bnn   (Expression 2)

For the approximate line for pulsation characteristics, the relationshipof Expression 2 above holds. This relational expression is an errorprediction expression for predicting the pulsation error Err using thepulsation amplitude Pa, and in this error prediction formula, Ann is aslope of the approximate line and Bnn is the intercept. In the pulsationcharacteristics, the pulsation error Err corresponds to a correctionparameter. The approximate line for the pulsation characteristics may beillustrated by a curve. In this case, the expression representing theapproximate line for the pulsation characteristics includes a quadraticfunction or a function of second order or higher such as a cubicfunction.

The pulsation characteristics are set for each combination of theaverage air amount Gave and the pulsation frequency F. In the mapillustrated in FIG. 12, a slope Ann and an intercept Bnn indicatingpulsation characteristics are set for each window illustrating thecombination of the average air amount Gave and the pulsation frequencyF. When such a map illustrating the relationship between the average airamount Gave and the pulsation frequency F and the pulsationcharacteristics is referred to as a reference map, this reference map isa two-dimensional map and is stored in the storage device of theprocessing unit 45. In the reference map, the pulsation characteristicsare set for each of the average air amount Gave and the pulsationfrequency F with respect to predetermined values defined in advance. Thereference map may be a map having three or more dimensions such as athree-dimensional map or a four-dimensional map. For example, athree-dimensional map illustrating the relationship between the averageair amount Gave and the pulsation frequency F and the pulsationamplitude Pa may be used as a reference map.

In FIG. 12, map values of the average air amount Gave set in thereference map are denoted by G1 to Gn, and map values of the pulsationfrequency F are denoted by F1 to Fn. The reference map may be referredto as a correction map, and the reference information may be referred toas correction information.

The reference map can be created by confirming the relationship betweenthe pulsation amplitude Pa and the pulsation error Err correlated withthe pulsation amplitude Pa by experiments, simulations, or the likeusing an actual machine. That is, it can be said that the pulsationerror Err is a value obtained for each pulsation amplitude Pa when anexperiment or simulation using an actual machine is performed bychanging the value of the pulsation amplitude Pa. The other maps in thefollowing embodiments can also be created by experiments, simulations,or the like using an actual machine, like the reference map.

The correction amount calculation unit 60 a calculates the correctionamount Q using the pulsation error Err calculated by the pulsation errorcalculation unit 60. The correction amount calculation unit 60 a targetsthe measurement period for calculation, and calculates the correctionamount Q by using the correlation information such as a map illustratingthe correlation between the pulsation error Err and the correctionamount Q. The correction amount Q is a value indicating the ratio of thecorrection to the output value. For example, when the output value iscorrected so that the air flow rate becomes large, the correction amountQ becomes larger than 1, and when the output value is corrected so thatthe air flow rate becomes small, the correction amount Q becomes smallerthan 1. The correction ratio can also be referred to as a gain.

The pulsation error correction unit 61 corrects the air flow rate sothat the pulsation error Err becomes small by using the sampling valueconverted by the conversion table 54 and the correction amount Qcalculated by the correction amount calculation unit 60 a. That is, thepulsation error correction unit 61 corrects the air flow rate so thatthe air flow rate affected by the pulsation approaches the true air flowrate. Here, the average air amount Gave is employed as the correctiontarget of the air flow rate.

The pulsation error correction unit 61 corrects an output value S1before correction with the correction amount Q and calculates the outputvalue S2 after correction. In the present embodiment, the output valueS2 after correction is calculated by multiplying the output value S1before correction by the correction amount Q. In this case, therelationship S2=S1×Q holds. For example, when the correction amount Q islarger than 1, the output value S2 after correction becomes larger thanthe output value S1 before correction, as illustrated in FIG. 13A. Thepulsation error correction unit 61 targets the measurement period forcalculation, and the output value S1 before correction includes at leastthe upper extreme value Ea and the lower extreme value Eb.

The correction circuit 50 outputs the output value S2 after correctioncalculated by the pulsation error correction unit 61 to the outputcircuit 62. The output circuit 62 outputs the output value S2 aftercorrection to the ECU 46. The ECU 46 uses the output value S2 aftercorrection input from the output circuit 62 to calculate the averagevalue of the output value S2 after correction as the corrected averageair amount Gave2. For example, when the correction amount Q is largerthan 1, as illustrated in FIG. 13A, the average air amount Gave2 aftercorrection is larger than the average air amount Gave1 beforecorrection.

For example, as illustrated in FIG. 13B, an upper extreme value Ean dueto noise may occur in the waveform representing a time change of theoutput value of the sensing unit 22 or a conversion value of theconversion table 54. This noise is caused by air turbulence, notelectrical noise. Specifically, due to switching of each stroke of thecombustion cycle, such as switching from an intake stroke to acompression stroke in any cylinder of the internal combustion engine,the flow rate of the intake air flowing through the intake passage 12becomes unstable at the time of the switching. Thus, the air flow ratemeasured by the sensing unit 22 also becomes unstable at the time ofswitching of each stroke of the combustion cycle. Due to such airturbulence, in the waveform illustrated in FIG. 13B, the upper extremevalue Ean due to noise appears immediately after the upper extreme valueEa1. That is, a portion that slightly repeats increasing and decreasingappears in the waveform.

The upper extreme value determination unit 56 negatively determines andcancels the upper extreme value Ean due to noise because it is not theupper extreme value used for calculating the upper extreme interval Wa.Specifically, the upper extreme value determination unit 56 determineswhether or not the output value has become equal to or less than thelower threshold Ee during a period from the upper extreme timing ta1when the upper extreme value Ea1 has previously appeared to a timingwhen the upper extreme value Ean at present time has appeared. Upondetermining that the output value remains to be more than the lowerthreshold Ee, the upper extreme value determination unit 56 regards theupper extreme value Ean at present time as due to noise and cancels theupper extreme value Ean. Therefore, the upper extreme value Ean due tonoise is not erroneously detected as the upper extreme value.

However, for example, as illustrated in FIG. 13C, a lower extreme valueEbn due to harmonics may occur in the waveform representing the timechange of the output value of the sensing unit 22 or the conversionvalue of the conversion table 54. That is, due to the influence ofharmonics, a valley portion like a crack may appear in the waveform, andthe output value may change suddenly.

In this case, the output value has become equal to or less than thelower threshold Ee during the period from the upper extreme timing ta1when the upper extreme value Ea1 has previously appeared to the timingwhen the upper extreme value Ean at present time has appeared, the upperextreme value Ean at present time is not canceled and is erroneouslydetected as an upper extreme value.

For example, as illustrated in FIG. 13D, a steep output change may occurin a waveform representing a time change of the output value of thesensing unit 22 or the conversion value of the conversion table 54. Forexample, when the vehicle is accelerating, the output value may changesuddenly and greatly.

In this case, during the period from the upper extreme timing ta3 whenthe upper extreme value Ea3 has previously appeared to the timing whenthe upper extreme value Ean at present time has appeared, the outputvalue becomes higher without becoming equal to or less than the lowerthreshold Ee. If the output value becomes high without becoming equal toor less than the lower threshold Ee in this manner, there is a problemthat the upper extreme value Ean detected from the next time onward willbe canceled one after another and will not be detected as the upperextreme value.

In order to solve these issues, the upper extreme value determinationunit 56 of the present embodiment carries out a process of updating thelower threshold Ee so that the value of the lower threshold Ee changes.

As illustrated in FIG. 13E, the memory of the present embodiment storesa map in which the pulsation amplitude Pa, the pulsation frequency F,and the average air amount Gave are associated with a reference value ofthe lower threshold Ee. This map is a three-axis map centered on thethree variables of a pulsation amplitude Pa, a pulsation frequency F,and an average air amount Gave.

The upper extreme value determination unit 56 updates the lowerthreshold Ee with reference to this map. The reference value may be aconstant or a function. Specifically, the reference value of the lowerthreshold Ee corresponding to the pulsation amplitude Pa, the pulsationfrequency F, and the average air amount Gave is updated as a new lowerthreshold Ee.

As the engine speed increases, the pulsation frequency F also increases,and harmonic noise is likely to be included in the output value of thesensing unit 22. Thus, for example, the lower threshold Ee can be set tobe a smaller value as the pulsation frequency F is larger. When theaccelerator is depressed and the engine speed increases, the average airamount Gave also increases, and the output value of the sensing unit 22tends to include harmonic noise. Thus, for example, the lower thresholdEe can be set to be a smaller value as the average air amount Gave islarger. When the engine speed reaches a specific speed, the pulsationamplitude Pa may increase. Therefore, for example, the lower thresholdEe can be set to be smaller as the pulsation amplitude Pa is larger. Themap stores the reference value of an optimum lower threshold Ee obtainedby the experiment.

FIG. 13F is a flowchart illustrating a procedure of processing by theupper extreme value determination unit 56. The process illustrated inFIG. 13F is repeatedly executed by a microcomputer during the period inwhich the output value is input to the correction circuit 50. Themicrocomputer processing here means processing in a digital circuit, andcan be processed by, for example, a DSP or hard logic. The DSP is anabbreviation for digital signal processor. First, in step S5, the flowrate data is updated. Specifically, new flow rate data is read. In thenext step S10, it is determined whether or not the sampling value atpresent time is increasing in the flow rate in the waveform of thesampling value converted by the conversion table 54.

When it is determined that the value is increasing, the flow rate dataand the lower threshold Ee are updated as a flow rate increase detectionstate in the next step S11. Specifically, the pulsation amplitude Pa,the pulsation frequency F, and the average air amount Gave arespecified, the reference value of the lower threshold Ee correspondingto these is specified using the map, and the lower threshold Ee isspecified on the basis of the reference value of the lower threshold Ee.This lower threshold Ee is updated as a new lower threshold Ee.

In the next step S12, it is determined whether or not the flow rate haschanged from increase to decrease. If it is determined that the flowrate has changed to decrease in step S12, peak detection is performed innext step S18. Specifically, the sampling value at present time isdetected as the upper extreme value Ea. If it is not determined that theflow rate has changed to decrease in step S12, the process returns tostep 11.

After the processing of step S18, the flow rate data and the lowerthreshold Ee are updated as a flow rate decrease detection state in stepS19. Specifically, the pulsation amplitude Pa, the pulsation frequencyF, and the average air amount Gave are specified, the reference value ofthe lower threshold Ee corresponding to these is specified using themap, and the lower threshold Ee is specified on the basis of thereference value of the lower threshold Ee. This lower threshold Ee isupdated as a new lower threshold Ee.

In the next step S20, it is determined whether or not the flow rate haschanged from decrease to increase. If it is determined in step S20 thatthe flow rate has changed to increase, in the next step S24, it isdetermined whether or not the sampling value at present time is equal toor less than the predetermined lower threshold Ee. If it is notdetermined in step S20 that the flow rate has changed to increase, or ifit is determined in step S24 that the sampling value at present time isnot equal to or less than the lower threshold Ee, the process returns tostep S19.

If it is determined that the threshold is equal to or less than thelower threshold Ee, the execution is restarted from the processing ofstep S10. Therefore, when the step S10 is restarted in this manner, theflow rate has just been switched to increase, and thus it is determinedthat the flow rate is increased in the step S10. In steps S11 and S12,the process waits until the flow rate switches from increase todecrease, and in step S18, the next upper extreme value Ea is detected.Thus, if the output value remains to be more than the predeterminedlower threshold Ee after the upper extreme value is detected once, thenext upper extreme value is negatively determined.

As described above, the lower threshold Ee is updated in step S11 andstep S19. Specifically, the pulsation amplitude Pa, the pulsationfrequency F, and the average air amount Gave are specified, and thereference value of the lower threshold Ee corresponding to these isupdated as a new lower threshold Ee.

Thus, the lower threshold Ee in FIG. 13C can be made lower than thelower extreme value Ebn due to noise. In this case, the sampling valueat present time will be cancelled. Therefore, it is possible to preventerroneous detection of the lower extreme value Ebn due to noise.

It is also possible to make the lower threshold Ee in FIG. 13D largerthan the lower extreme value Ebn. In this case, the upper extreme valueEan will be detected.

Thus, even when a steep output change occurs, the lower threshold Ee canbe updated and the upper extreme value Ean can be detected correctly.

As described above, the measurement control device of the presentembodiment includes the sensing unit 22 that outputs a signal accordingto the air flow rate and a pulsation state calculation unit thatcalculates a pulsation state that is a state of pulsation generated inthe air flow rate using the output value of the sensing unit 22. Themeasurement control device includes a pulsation error correction unit 61that corrects the air flow rate using the pulsation state calculated bythe pulsation state calculation unit. The pulsation state calculationunit has an upper extreme value determination unit 56 that, when theoutput value when a change mode of the output value switches fromincrease to decrease is referred to as an upper extreme value Ea,determines whether or not the output value has become the upper extremevalue Ea. Moreover, the pulsation state calculation unit has a frequencycalculation unit 59 that calculates the pulsation frequency F ofpulsation generated in the air flow rate on the basis of the timeinterval at which the output value becomes the upper extreme value Ea.When the output value remains to be more than the predetermined lowerthreshold Ee during a period from a timing when the upper extreme valueEa has previously appeared to a timing when the upper extreme value Eahas presently appeared in the waveform representing a time change of theoutput value, the upper extreme value determination unit 56 negativelydetermines and cancels the upper extreme value Ea that has presentlyappeared. Moreover, the upper extreme value determination unit 56updates the lower threshold Ee on the basis of the air flow ratespecified on the basis of the output value, the pulsation frequency F,and the pulsation amplitude Pa specified on the basis of the outputvalue.

With such a configuration, the lower threshold Ee is updated on thebasis of the air flow rate specified on the basis of the output value,the pulsation frequency F, and the pulsation amplitude Pa specified onthe basis of the output value, and thus false detection of the upperextreme value Ea is reduced. Therefore, the correction accuracy of theair flow rate can be improved.

The upper extreme value determination unit 56 updates the lowerthreshold Ee using a map in which the air flow rate, the pulsationfrequency F, and the pulsation amplitude Pa are associated with thereference value of the lower threshold Ee.

In this manner, the upper extreme value determination unit 56 can updatethe lower threshold Ee using the map in which the air flow rate, thepulsation frequency F, and the pulsation amplitude Pa and the referencevalue of the lower threshold Ee are associated with each other.

The measurement control device of the present embodiment includes thesensing unit 22 that outputs a signal according to the air flow rate anda pulsation state calculation unit that calculates a pulsation statethat is a state of pulsation generated in the air flow rate using theoutput value of the sensing unit 22. The measurement control deviceincludes a pulsation error correction unit 61 that corrects the air flowrate using the pulsation state calculated by the pulsation statecalculation unit. The pulsation state calculation unit has an upperextreme value determination unit 56 that, when the output value when achange mode of the output value switches from increase to decrease isreferred to as an upper extreme value Ea, determines whether or not theoutput value has become the upper extreme value Ea. The pulsation statecalculation unit has the frequency calculation unit 59 that calculatesthe pulsation frequency F of the pulsation generated in the air flowrate on the basis of a time interval at which the output value becomesthe upper extreme value Ea. When the output value remains to be morethan the predetermined lower threshold Ee during a period from a timingwhen the upper extreme value has previously appeared to a timing whenthe upper extreme value has presently appeared in a waveformrepresenting a time change of the output value, the upper extreme valuedetermination unit 56 negatively determines and cancels the upperextreme value Ea that has presently appeared. Moreover, the upperextreme value determination unit 56 updates the lower threshold Ee onthe basis of the reference value of the lower threshold Ee that changesaccording to the pulsation state.

With such a configuration, the lower threshold Ee is updated on thebasis of the reference value of the lower threshold Ee that changesaccording to the pulsation state, and thus false detection of the upperextreme value Ea is reduced. Therefore, the correction accuracy of theair flow rate can be improved.

The upper extreme value determination unit 56 updates the lowerthreshold Ee using a map in which the reference value of the lowerthreshold Ee is associated according to the pulsation state.

In this manner, the lower threshold Ee can be updated using the map inwhich the reference value of the lower threshold Ee is associatedaccording to the pulsation state.

The frequency calculation unit 59 has a frequency limiting function thatlimits a change amount in the pulsation frequency F to be equal to orless than a predetermined maximum frequency change amount.

Therefore, for example, even when a high-frequency noise component isadded to the output value of the sensing unit 22, the change amount inthe pulsation frequency F is limited, so that the influence of noise canbe suppressed.

The frequency calculation unit 59 includes an operation unit 59 a thatsets enable or disable of the frequency limiting function. This makes itpossible to enable or disable the frequency limiting function.

In the present embodiment, as illustrated in FIG. 13E, a map in whichthe pulsation amplitude Pa, the pulsation frequency F, and the averageair amount Gave and the reference value of the lower threshold Ee areassociated with each other is stored in the memory in advance, and thelower threshold Ee is updated by referring to the map.

On the other hand, as illustrated in FIG. 13G, a map in which thepulsation amplitude Pa and the pulsation frequency F and the referencevalue of the lower threshold Ee are associated with each other may bestored in the memory in advance, and the lower threshold Ee may beupdated by referring to the map.

A map in which at least one of the pulsation amplitude Pa, the pulsationfrequency F, or the average air amount Gave is associated with thereference value of the lower threshold Ee may be stored in the memory inadvance, and the lower threshold Ee may be updated by referring to themap.

(Second Embodiment)

A measurement control device according to a second embodiment will bedescribed with reference to FIGS. 14 to 16. In the first embodiment, thecorrection circuit 50 has only one path for inputting the output valueof the sensing unit 22 to the pulsation amplitude calculation unit 58,but in the second embodiment, there are two routes to input the outputvalue to the pulsation amplitude calculation unit 58. In the presentembodiment, differences from the first embodiment will be mainlydescribed.

As illustrated in FIG. 14, the correction circuit 50 has a first path 70a that inputs an output value converted in the first conversion table 54to the pulsation amplitude calculation unit 58, and a second path 70 bthat inputs an output value before conversion in the first conversiontable 54 to the pulsation amplitude calculation unit 58. In FIG. 14, anillustration of a part of the first path 70 a is omitted by a symbol A.

In addition to the same functional blocks as those in the firstembodiment, the correction circuit 50 includes a disturbance removalunit 71, a response compensation unit 72, an amplitude reduction filterunit 73, a second conversion table 74, a disturbance removal filter unit75, a sampling number increasing unit 76, a switch unit 77, and a minuscut unit 78. In the second embodiment, a conversion table 54substantially the same as that described in the first embodiment will bereferred to as a first conversion table 54, and a conversion table 74 tobe described in the second embodiment will be referred to as a secondconversion table 74.

The disturbance removal unit 71 is a functional block that is providedbetween the variation adjustment unit 53 and the first conversion table54, and to which an output value processed by the variation adjustmentunit 53 is input. The disturbance removal unit 71 is a sudden changelimiting unit that limits a sudden change in the output value so largethat the rate of change with respect to the output value at previoustime exceeds a predetermined reference value, and limits the changeamount to a predetermined value, for example. For example, when noiseillustrated in FIG. 15 is included in the output value, this noise isremoved by the disturbance removal unit 71.

The response compensation unit 72 is a functional block that is providedbetween the disturbance removal unit 71 and the first conversion table54, and to which an output value processed by the disturbance removalunit 71 is input. The response compensation unit 72 is a filter thatcauses the output value to faithfully reproduce a sudden change in theair flow rate actually detected by the sensing unit 22, and is formedby, for example, a high-pass filter. An output value compensated by theresponse compensation unit 72 has a state in which the response isadvanced in time and the frequency range is wider than the output valuebefore compensation.

The amplitude reduction filter unit 73 is a functional block that isprovided between the first conversion table 54 and the pulsation errorcorrection unit 61, and to which an output value processed by the firstconversion table 54 is input. The amplitude reduction filter unit 73 isa filter unit that blunts and reduces the pulsation amplitude Pa of theoutput value, and is formed by, for example, a low-pass filter.Processing of the amplitude reduction filter unit 73 is performed afterprocessing of the first conversion table 54, and thus the average airamount Gave calculated using the output value does not change.

The first path 70 a is connected between the first conversion table 54and the pulsation error correction unit 61, and the second path 70 b isconnected between the disturbance removal unit 71 and the responsecompensation unit 72. Both of these paths 70 a and 70 b are connected tothe pulsation amplitude calculation unit 58 via the switch unit 77. Theswitch unit 77 is a switching unit that selectively connects the firstpath 70 a and the second path 70 b to the pulsation amplitudecalculation unit 58. When the switch unit 77 is in a first state, thepulsation amplitude calculation unit 58 is connected to the first path70 a but is blocked from the second path 70 b. When the switch unit 77is in a second state, the pulsation amplitude calculation unit 58 isconnected to the second path 70 b but is blocked from the first path 70a.

The switch unit 77 is set to one of the first state and the second stateat the time of manufacturing the air flow meter 10, and basically holdsthe state after being mounted on the vehicle. The state of the switchunit 77 may be switched according to the engine operating state or thelike after being mounted on the vehicle.

The second conversion table 74 is a functional block that is providedbetween the disturbance removal unit 71 and the switch unit 77 in thesecond path 70 b, and to which an output value processed by thedisturbance removal unit 71 is input. Unlike the first conversion table54, the second conversion table 74 converts a sampling value acquired bythe sampling unit 52 into an air flow rate at a stage before processingof the response compensation unit 72 is performed.

The disturbance removal filter unit 75 is a functional block that isprovided between the second conversion table 74 and the upper extremevalue determination unit 56 in the path branched from the second path 70b, and to which an output value processed by the second conversion table74 is input. The disturbance removal filter unit 75 is a filter unitthat blunts and removes an output value contained in a higher-ordercomponent that is a harmonic component, and is formed by, for example, alow-pass filter. The disturbance removal filter unit 75 can variably seta filter constant.

The sampling number increasing unit 76 is a functional block that isprovided between the disturbance removal filter unit 75 and the upperextreme value determination unit 56, and to which an output valueprocessed by the disturbance removal filter unit 75 is input. Thesampling number increasing unit 76 is an up-sampling unit that increasesthe sampling value acquired by the sampling unit 52, and has a highertime resolution than the sampling unit 52. The sampling numberincreasing unit 76 is formed by a filter such as a variable filter or aCIC filter.

The upper extreme value determination unit 56 determines whether or notthe sampling value converted in the conversion table 54 is an upperextreme value Ea. The upper extreme value Ea is a sampling value at atiming when the output value switches from increase to decrease.

When the output value remains to be more than the predetermined lowerthreshold Ee during a period from a timing when the upper extreme valueEa has previously appeared to a timing when the upper extreme value Eahas presently appeared in the waveform representing a time change of theoutput value, the upper extreme value determination unit 56 negativelydetermines and cancels the upper extreme value Ea that has presentlyappeared. Moreover, the upper extreme value determination unit 56specifies the reference value of the lower threshold Ee by referring tothe map in which the pulsation amplitude Pa, the pulsation frequency F,and the average air amount Gave are associated with the reference valueof the lower threshold Ee, and the lower threshold Ee is updated on thebasis of the reference value of this lower threshold.

The frequency calculation unit 59 adds the calculated pulsationfrequency F to the pulsation error calculation unit 60 and outputs thecalculated pulsation frequency F to the disturbance removal filter unit75. The disturbance removal filter unit 75 feedback-controls an optimumfilter constant using the pulsation frequency F from the frequencycalculation unit 59.

The minus cut unit 78 cuts a minus output value S2 out of the outputvalue S2 after correction, and calculates an output value S3 aftercutting. As illustrated in FIG. 16, when the output value S2 aftercorrection contains a minus value, which is a negative value, the minusvalue is cut by the minus cut unit 78 to be zero, so that the outputvalue S3 after cutting does not contain any negative values. On theother hand, for a plus value, which is a positive value, the outputvalue S2 after correction and the output value S3 after cutting are thesame values. As described above, in the housing 21, the measurementoutlet 36 is provided at a position where a backflow generated in theintake passage 12 is less likely to flow in from the measurement outlet36, but when entrance of the backflow from the measurement outlet 36does not always become zero. In this case, the air flow rate of thebackflow entering from the measurement outlet 36 becomes unstable, andit becomes difficult to measure the air flow rate with high accuracy.Accordingly, by performing processing of the minus cut unit 78, themeasurement accuracy of the air flow rate can be improved.

In the correction circuit 50, in addition to the average air amountGave2 after correction calculated by the pulsation error correction unit61 and the output value S2 after correction, the output value S3 aftercutting calculated by the minus cut unit 78 is output to the outputcircuit 62. The output circuit 62 outputs an average air amount Gave2after correction, the output value S2 after correction, and the outputvalue S3 after correction to the ECU 46.

In the present embodiment, similar effects exhibited by componentscommon to the above-described first embodiment can be obtained as in thefirst embodiment.

The measurement control device of the present embodiment includes adisturbance removal filter unit 75 that removes a predeterminedfrequency component from the signal output from the sensing unit 22. Theupper extreme value determination unit 56 specifies the lower thresholdEe using the output value of the signal transmitted through thedisturbance removal filter unit 75.

Therefore, even when high frequency noise is added to the output valueof the sensing unit 22, it is possible to specify the lower threshold Eewithout being affected by the high frequency noise.

The disturbance removal filter unit 75 includes a low-pass filter thatremoves high-frequency components. In this manner, the disturbanceremoval filter unit 75 can include a low-pass filter.

(Third Embodiment)

A measurement control device according to a third embodiment will bedescribed with reference to FIGS. 17 to 18A. In the first embodiment,the correction circuit 50 has the upper extreme value determination unit56, but in the third embodiment, the correction circuit 50 has a lowerextreme value determination unit 81. In the present embodiment,differences from the first embodiment will be mainly described.

As illustrated in FIG. 17, the lower extreme value determination unit 81is provided between the conversion table 54 and the frequencycalculation unit 59 in the correction circuit 50. The lower extremevalue determination unit 81 determines whether or not a sampling valueprocessed by the conversion table 54 is a lower extreme value Eb. Asdescribed above, the lower extreme value Eb is the sampling value at atiming when an output value switches from decrease to increase. Thelower extreme value determination unit 81 acquires a timing when thesampling value becomes the lower extreme value Eb as the lower extremetiming tb, and causes the lower extreme value Eb to be stored in thestorage device of the processing unit 45. The lower extreme valuedetermination unit 81 outputs information including the lower extremetiming tb as timing information indicating a pulsation cycle to theaverage air amount calculation unit 57, the pulsation amplitudecalculation unit 58, and the frequency calculation unit 59. The factthat the output value becomes the lower extreme value Eb corresponds toa specific condition, and the lower extreme value determination unit 81and the frequency calculation unit 59 correspond to the pulsation statecalculation unit.

The lower extreme value determination unit 81 determines whether or notthe sampling value converted in the conversion table 54 is the lowerextreme value Eb. The lower extreme value Eb is the sampling value atthe timing when the output value switches from decrease to increase.

When the output value remains to be less than a predetermined upperthreshold Ef during a period from a timing when the lower extreme valueEb has previously appeared to a timing when the lower extreme value Ebhas presently appeared in the waveform representing a time change of theoutput value, the lower extreme value determination unit 81 negativelydetermines and cancels the lower extreme value Eb that has presentlyappeared. Further, the lower extreme value determination unit 81specifies a reference value of the lower threshold Ee on the basis ofthe physical quantity, the pulsation frequency F, and the pulsationamplitude Pa that correlate with the average air amount Gave, andupdates the lower threshold Ee on the basis of the reference value ofthe lower threshold Ee. The lower extreme value determination unit 81,as does the upper extreme value determination unit 56, causes a map inwhich the pulsation amplitude Pa, the pulsation frequency F, and theaverage air amount Gave and a reference value of the upper threshold Efare associated with each other to be stored in the memory in advance,and updates the upper threshold Ef by referring to the map.Specifically, the reference value of the upper threshold Efcorresponding to the pulsation amplitude Pa, the pulsation frequency F,and the average air amount Gave is updated as a new upper threshold Ef.

The frequency calculation unit 59 uses the timing information from thelower extreme value determination unit 81 to calculate an interval atwhich the sampling value becomes the lower extreme value Eb as a lowerextreme interval Wb, and uses this lower extreme interval Wb tocalculate the pulsation frequency F. For example, as illustrated in FIG.18A, when the sampling value becomes the lower extreme value Eb and thenthe sampling value becomes the next lower extreme value Eb, the previouslower extreme value Eb will be referred to as the first lower extremevalue Eb1, and the next lower extreme value Eb will be referred to asthe second lower extreme value Eb2. In this case, the frequencycalculation unit 59 uses a first lower extreme timing tb1 at which thesampling value becomes the first lower extreme value Eb1 and a secondlower extreme timing tb2 at which the sampling value becomes the secondlower extreme value Eb2, to calculate the lower extreme interval Wb thatis the interval between the lower extreme timings tb1 and tb2. Forexample, the pulsation frequency F is calculated using the relationshipF[Hz]=1/Wb[s].

For the period from the first lower extreme timing tb1 to the secondlower extreme timing tb2, the minimum pulsation value Gmin is thesmaller one of the first lower extreme value Eb1 and the second lowerextreme value Eb2. When these lower extreme values Eb1 and Eb2 are thesame value, that value becomes the minimum pulsation value Gmin. Theaverage value of the first lower extreme value Eb1 and the second lowerextreme value Eb2 may be the minimum pulsation value Gmin.

As described above, the measurement control device of the presentembodiment includes the sensing unit 22 that outputs a signal accordingto the air flow rate and a pulsation state calculation unit thatcalculates a pulsation state that is a state of pulsation generated inthe air flow rate using the output value of the sensing unit 22. Themeasurement control device includes a pulsation error correction unit 61that corrects the air flow rate using the pulsation state calculated bythe pulsation state calculation unit. The pulsation state calculationunit has a lower extreme value determination unit 81 that, when theoutput value when a change mode of the output value switches fromdecrease to increase is referred to as the lower extreme value Eb,determines whether or not the output value has become the lower extremevalue Eb. When the output value remains to be less than thepredetermined upper threshold Ef during a period from a timing when thelower extreme value Eb has previously appeared to a timing when thelower extreme value Eb has presently appeared in the waveformrepresenting a time change of the output value, the lower extreme valuedetermination unit 81 negatively determines and cancels the lowerextreme value Eb that has presently appeared. Moreover, the upperthreshold Ef is updated on the basis of at least one of the air flowrate specified on the basis of the output value, the pulsation frequencyF specified on the basis of the output value, or the pulsation amplitudePa specified on the basis of the output value.

With such a configuration, the upper threshold Ef is updated on thebasis of at least one of the air flow rate specified on the basis of theoutput value, the pulsation frequency F specified on the basis of theoutput value, or the pulsation amplitude Pa specified on the basis ofthe output value, and thus false detection of the lower extreme value Ebis reduced. Therefore, the correction accuracy of the air flow rate canbe improved.

The measurement control device includes the sensing unit 22 that outputsa signal according to the air flow rate, and a pulsation statecalculation unit that calculates a pulsation state that is a state ofpulsation generated in the air flow rate using the output value of thesensing unit 22. The measurement control device includes a pulsationerror correction unit 61 that corrects the air flow rate using thepulsation state calculated by the pulsation state calculation unit. Thepulsation state calculation unit has a lower extreme value determinationunit 81 that, when the output value when a change mode of the outputvalue switches from decrease to increase is referred to as the lowerextreme value Eb, determines whether or not the output value has becomethe lower extreme value Eb. The pulsation state calculation unit has afrequency calculation unit 59 that calculates the pulsation frequency Fof the pulsation generated in the air flow rate on the basis of the timeinterval in which the output value becomes the lower extreme value Eb.When the output value remains to be less than the predetermined upperthreshold Ef during a period from a timing when the lower extreme valuehas previously appeared to a timing when the lower extreme value haspresently appeared in the waveform representing a time change of theoutput value, the lower extreme value determination unit 81 negativelydetermines and cancels the lower extreme value that has presentlyappeared. Moreover, the lower extreme value determination unit 81updates the upper threshold Ef on the basis of the reference value ofthe upper threshold Ef that changes according to the pulsation state.

With such a configuration, the upper threshold Ef is updated on thebasis of the reference value of the upper threshold Ef that changesaccording to the pulsation state, and thus false detection of the lowerextreme value Eb is reduced. Therefore, the correction accuracy of theair flow rate can be improved.

(Fourth Embodiment)

A measurement control device according to a fourth embodiment will bedescribed. The upper extreme value determination unit 56 of the firstembodiment causes a map in which the pulsation amplitude Pa, thepulsation frequency F, and the average air amount Gave and the referencevalue of the lower threshold Ee are associated with each other to bestored in the memory in advance, and updates the lower threshold Ee byreferring to the map thereof.

On the other hand, the upper extreme value determination unit 56 of thepresent embodiment causes a function that takes at least one of thepulsation amplitude Pa, the pulsation frequency F, or the average airamount Gave as a variable, and calculates the lower threshold Ee to bestored in the memory in advance, and updates the lower threshold Eeusing the function. In this manner, the upper extreme valuedetermination unit 56 can also update the lower threshold Ee using afunction.

(Fifth Embodiment)

A measurement control device according to a fifth embodiment will bedescribed. The measurement control device of the present embodiment hasthe same configuration as that of the measurement control device of thefirst embodiment. The upper extreme value determination unit 56 of thefirst embodiment updates the lower threshold Ee using a map in which thepulsation amplitude Pa, the pulsation frequency F, and the average airamount Gave are associated with the reference value of the lowerthreshold Ee. On the other hand, the upper extreme value determinationunit 56 of the present embodiment updates the lower threshold Ee byusing the lower threshold Ee used for determining the upper extremevalue Ea in a period from before the predetermined period to the timingwhen the upper extreme value Ea has presently appeared. In the followingdescription, the reference sign Ee of the lower threshold may beomitted.

As illustrated in FIG. 18B, an output value of the sensing unit 22 at apredetermined timing ta11 is Org_n−1, and a lower threshold at thepredetermined timing ta11 is Out_n−1. An output value of the sensingunit 22 at a timing ta12 after a sampling interval Δt has elapsed fromthe predetermined timing ta11 is Org_n, and a lower threshold is Out_n,a sampling interval is Δt, and a time constant is T at the timing ta12.In the following description, the timing ta12 after the samplinginterval Δt has elapsed from the predetermined timing ta11 is referredto as “present timing ta12” for convenience of description.

The upper extreme value determination unit 56 calculates the lowerthreshold Out_n at the present timing ta12 using Mathematical Expression1 below.

[Expression 1]

Out_n=(Org_n−Out_n−1)×(1−e ^((−Δt/T)))+Out_n−1   Mathematical Expression1

The upper extreme value determination unit 56 updates the lowerthreshold Out_n at the present timing ta12 to a value calculated usingMathematical Expression 1. A timing for updating the lower threshold isthe same as S11 and S19 in FIG. 13F.

The lower threshold Out_n at the present timing ta12 is updated on thebasis of a difference between the output value Org_n of the sensing unit22 at the present timing ta12 and the lower threshold Out_n−1 at thepredetermined timing ta11.

The lower threshold Out_n is a value obtained by applying a first-orderresponse delay to the output value of the sensing unit 22. That is, thelower threshold Out_n is updated so as to slowly follow the output valueof the sensing unit 22 while being delayed.

FIG. 18C illustrates waveforms of the output value G of the sensing unit22 and the lower threshold Ee updated using Mathematical Expression 1.As illustrated in FIG. 18C, the lower threshold Ee changes so as tofollow the output value G of the sensing unit 22. The lower extremevalue Eb and the upper extreme value Ean in FIG. 18C are due to harmonicnoise.

As illustrated in FIG. 18C, the lower extreme value Eb remains to bemore than the predetermined lower threshold Ee by updating the lowerthreshold Out_n so as to follow the output value G of the sensing unit22. Therefore, the upper extreme value determination unit 56 negativelydetermines and cancels the upper extreme value Ean due to the harmonicnoise. Therefore, the toughness against harmonic noise can be improved.

As described above, the measurement control device of the presentembodiment includes the sensing unit 22 that outputs a signal accordingto the air flow rate and a pulsation state calculation unit thatcalculates a pulsation state that is a state of pulsation generated inthe air flow rate using the output value of the sensing unit 22. Themeasurement control device includes a pulsation error correction unit 61that corrects the air flow rate using the pulsation state calculated bythe pulsation state calculation unit. The pulsation state calculationunit has an upper extreme value determination unit 56 that, when theoutput value when a change mode of the output value switches fromincrease to decrease is referred to as an upper extreme value Ea,determines whether or not the output value has become the upper extremevalue Ea. The pulsation state calculation unit has the frequencycalculation unit 59 that calculates the pulsation frequency F of thepulsation generated in the air flow rate on the basis of a time intervalat which the output value becomes the upper extreme value Ea. When theoutput value remains to be more than the predetermined lower thresholdEe during a period from a timing when the upper extreme value Ea haspreviously appeared to a timing when the upper extreme value Ea haspresently appeared in the waveform representing a time change of theoutput value, the upper extreme value determination unit 56 negativelydetermines and cancels the upper extreme value Ea that has presentlyappeared. Moreover, the upper extreme value determination unit 56updates the lower threshold Ee by using the lower threshold Ee used fordetermining the upper extreme value Ea in a period from before apredetermined period to the timing when the upper extreme value haspresently appeared.

With such a configuration, the lower threshold Ee is updated by usingthe lower threshold Ee used for determining the upper extreme value Eain a period from before the predetermined period to a timing when theupper extreme value Ea has presently appeared, and thus false detectionof the extreme value Ea is reduced. Therefore, the correction accuracyof the air flow rate can be improved.

The measurement control device of the present embodiment includes thesampling unit 52 that samples output values at a predetermined samplinginterval. When the output value remains to be more than the lowerthreshold Ee during the period from the timing when the upper extremevalue has previously appeared to the timing when the upper extreme valuehas presently appeared in a waveform representing a time change of theoutput value, the upper extreme value determination unit 56 negativelydetermines and cancels the upper extreme value that has presentlyappeared. Further, the measurement control device updates the lowerthreshold Out_n used to determine the output value at present time onthe basis of a difference between the output value Org_n at present timesampled by the sampling unit 52 and the lower threshold Out_n−1 used ata time of determining the output value at previous time sampled by thesampling unit 52.

In this manner, the lower threshold Out_n used to determine the outputvalue at present time can be updated on the basis of a differencebetween the output value Org_n at present time sampled by the samplingunit 52 and the lower threshold Out_n−1 used at a time of determiningthe sampled output value at previous time.

(Sixth Embodiment)

A measurement control device according to a sixth embodiment will bedescribed with reference to FIGS. 18D and 18E. In the first embodiment,when an affirmative determination is made in step S12 of FIG. 13F, theprocess proceeds to step S18. On the other hand, in the presentembodiment, if an affirmative determination is made in step S12 of FIG.18D, the process proceeds to step S34. In step S34, it is determinedwhether or not the sampling value at present time is equal to or higherthan the lower threshold Ee during the period from a timing when theupper extreme value Ea has previously appeared to a timing when theupper extreme value Ea has presently appeared in the waveformrepresenting the time change of the output value.

When the sampling value at present time remains to be less than thelower threshold Ee in step S34, the process returns to step S11 toupdate the flow rate data and the lower threshold Ee. That is, the upperextreme value Ean that has presently appeared is negatively determinedand canceled.

When the sampling value at present time is equal to or higher than thelower threshold Ee, the process proceeds to the next step S18, and thesampling value at present time is detected as the upper extreme valueEa.

Therefore, as illustrated in FIG. 18E, when the upper extreme value Eanthat has presently appeared is equal to or less than the lower thresholdEe, the upper extreme value Ean that has presently appeared isnegatively determined and canceled.

As described above, when the output value becomes equal to or less thanthe lower threshold Ee during the period from the timing when the upperextreme value Ea has previously appeared to the timing when the upperextreme value Ea has presently appeared in the waveform representing thetime change of the output value, the upper extreme value determinationunit 56 negatively determines and cancels the upper extreme value Eanthat has presently appeared.

Therefore, when the output value becomes equal to or less than the lowerthreshold Ee, the upper extreme value Ean appearing this time can beprevented from being recognized as the upper extreme value Ea.

(Seventh Embodiment)

A measurement control device according to a seventh embodiment will bedescribed. In the measurement control device of the present embodiment,the frequency calculation unit 59 calculates a pulsation frequencyaverage value, which is an average of the pulsation frequency F during aperiod from before a predetermined period to the timing when the upperextreme value Ea has presently appeared. The pulsation error correctionunit 61 corrects the air flow rate using the pulsation frequency averagevalue calculated by the frequency calculation unit 59.

In this manner, by calculating the pulsation frequency average value,which is the average of the pulsation frequency F during the period frombefore the predetermined period to the timing when the upper extremevalue Ea has presently appeared, robustness against minute fluctuationsin the pulsation frequency F can be improved. Influence of noise on theoutput value of the sensing unit 22 can be reduced.

(Eighth Embodiment)

A measurement control device according to an eighth embodiment will bedescribed. In the measurement control device of the present embodiment,the frequency calculation unit 59 calculates a median value of thepulsation frequency F during a period from before a predetermined periodto the timing when the upper extreme value Ea has presently appeared.The pulsation error correction unit 61 corrects the air flow rate usingthe median value of the pulsation frequency F calculated by thefrequency calculation unit 59.

In this manner, by calculating the median value of the pulsationfrequency F during the period from before the predetermined period tothe timing when the upper extreme value Ea has presently appeared,robustness against minute fluctuation of the pulsation frequency F canbe improved. Influence of noise on the output value of the sensing unit22 can be reduced.

(Ninth Embodiment)

A measurement control device according to a ninth embodiment will bedescribed. In the sixth embodiment, when the output value becomes equalto or less than the lower threshold Ee during a period from before thepredetermined period to a timing when the upper extreme value Ea haspresently appeared, the upper extreme value determination unit 56negatively determines and cancels the upper extreme value Ean that haspresently appeared. On the other hand, in the present embodiment, thelower extreme value determination unit 81 is provided in place of theupper extreme value determination unit 56, and the lower extreme valuedetermination unit 81 updates the upper threshold using the upperthreshold used for determining the lower extreme value during a periodfrom before a predetermined period to a timing when the lower extremevalue has presently appeared.

The measurement control device of the present embodiment has a sensingunit 22 that outputs a signal according to the air flow rate, and apulsation state calculation unit that calculates a pulsation state thatis a state of pulsation generated in the air flow rate by using theoutput value of the sensing unit 22.

The measurement control device includes a pulsation error correctionunit 61 that corrects the air flow rate using the pulsation statecalculated by the pulsation state calculation unit.

The pulsation state calculation unit has a lower extreme valuedetermination unit 81 that, when the output value when a change mode ofthe output value switches from decrease to increase is referred to asthe lower extreme value Eb, determines whether or not the output valuehas become equal to or more than the lower extreme value Eb. Thepulsation state calculation unit has a frequency calculation unit 59that calculates the pulsation frequency F of the pulsation generated inthe air flow rate on the basis of the time interval in which the outputvalue becomes the lower extreme value Eb.

When the output value remains to be less than the predetermined upperthreshold Ef during the period from the timing when the lower extremevalue Eb has previously appeared to the timing when the lower extremevalue Eb has presently appeared in the waveform representing the timechange of the output value, the lower extreme value determination unit81 negatively determines and cancels the lower extreme value Eb that haspresently appeared. Moreover, the upper threshold Ef is updated by usingthe upper threshold Ef used for determining the lower extreme value Ebin the period from before the predetermined period to the timing whenthe lower extreme value Eb has presently appeared.

With such a configuration, the upper threshold Ef is updated by usingthe upper threshold Ef used for determining the lower extreme value Ebin the period from before the predetermined period to the timing whenthe lower extreme value Eb has presently appeared, and thus falsedetection of the lower extreme value Eb is reduced. Therefore, thecorrection accuracy of the air flow rate can be improved.

(Other Embodiments)

Although the plurality of embodiments according to the presentdisclosure has been described above, the present disclosure is notconstrued as being limited to the above embodiments, and can be appliedto various embodiments and combinations within the scope of the gist ofthe present disclosure.

As modification 1, the measurement outlet 36 may face the opposite sideof the inflow port 33 as does the outflow port 34. For example, themeasurement outlet 36 is provided between the inflow port 33 and theoutflow port 34 in the depth direction Z. In this configuration, themeasurement outlet 36 is formed on a convex portion protruding in thewidth direction X from an outer peripheral surface of the housing 21,the measurement outlet 36 is open toward a downstream side of the intakepassage 12 as is the case with the outflow port 34. In the intakepassage 12, air flowing in the forward direction along the outerperipheral surface of the housing 21 passes through the measurementoutlet 36, so that turbulence of air flow such as a vortex is likely tooccur around the measurement outlet 36. Thus, even if the measurementoutlet 36 faces the opposite side of the inflow port 33, it isconceivable that this backflow is less likely to flow into themeasurement outlet 36 when an air backflow occurs at the intake passage12.

On the other hand, also in this modification, the pulsation error Err iscalculated using the pulsation amplitude Pa. Thus, even if the backflowis less likely to flow into the measurement outlet 36 and the correctionaccuracy of the air flow rate is likely to decrease, the correctionaccuracy can be improved as in the first embodiment. In the firstembodiment, the measurement outlet 36 may be provided in the downstreamouter surface 24 c, so as to be open toward the side opposite to theinflow port 33.

As modification 2, in the housing 21, a part of the measurement outlet36 is provided in the upstream outer surface 24 b and the rest is notprovided in the intermediate outer surface 24 d, but the entiremeasurement outlet 36 may be provided on the upstream outer surface 24 bor the intermediate outer surface 24 d. When the entire measurementoutlet 36 is provided in the upstream outer surface 24 b, aconfiguration in which the measurement outlet 36 is open toward theopposite side of the outflow port 34 is achieved. When the entiremeasurement outlet 36 is provided in the intermediate outer surface 24d, a configuration in which the measurement outlet 36 is open in thewidth direction X is achieved. In this configuration, the openingdirection of the measurement outlet 36 is different from both theopening direction of the inflow port 33 and the opening direction of theoutflow port 34.

As modification 3, the bypass passage 30 may have the measurement path32 but does not necessarily have the passage path 31. In this case, themeasurement inlet 35 is formed on the outer surface of the housing 21,and the air flowing through the intake passage 12 flows from themeasurement inlet 35 into the bypass passage 30.

As modification 4, if at least a part of a narrow portion such as thedetection narrow portion 37 is provided upstream of the sensing unit 22in the measurement path 32, the narrow portion may be provided in thebranch path 32 a or the guide path 32 b. The detection narrow portion 37may have a pair of extension surfaces extending from an inner wallsurface of the housing body 24 toward the sensing unit 22 in the widthdirection X, and a flat surface extending over these extension surfacesand extending straight in the depth direction Z. The extension surfacemay be a surface extending straight in the width direction X, or may bea surface extending straight in a direction inclined with respect to thewidth direction X. The extension surface may be a curved surface curvedso as to bulge outward, or may be a curved surface curved so as to berecessed toward the inside. The detection narrow portion 37 may haveonly the extension surface on the upstream side of the pair of extensionsurfaces. In this configuration, the flat surface extends to adownstream side of the detection path 32 c.

As modification 5, the correction amount calculation unit 60 a maycalculate the correction amount Q in the same unit as the output valueS1 before correction such as the offset amount, instead of thecorrection amount Q indicating the correction ratio such as the gainamount. In this case, the pulsation error correction unit 61 calculatesthe output value S2 after correction by adding the correction amount Qto the output value S1 before correction. In the sixth embodiment, thecorrection amount calculation unit 60 a may calculate the correctionamount Q in the same unit as the average air amount Gave 1 beforecorrection. In this case, the pulsation error correction unit 61calculates the average air amount Gave3 after correction by adding thecorrection amount Q to the average air amount Gave1 before correction.

As modification 6, the correction circuit 50 includes at least two ofthe upper extreme value determination unit 56 of the first embodiment,the lower extreme value determination unit 81 of the third embodiment,an increase threshold determination unit 82 of the fourth embodiment, ora decrease threshold determination unit 83 of the fifth embodiment maybe provided. In this case, the frequency calculation unit 59 calculatesthe pulsation frequency F for each of determination results of at leasttwo of the upper extreme value determination unit 56, the lower extremevalue determination unit 81, the increase threshold determination unit82, or the decrease threshold determination unit 83, and calculates thepulsation frequency F by taking an average of these pulsationfrequencies F, or the like.

As modification 7, the processing unit 45 may process the output valuefrom the sensing unit 22 by a map, a function, a fast Fourier transform,or the like to calculate the pulsation frequency F.

As modification 8, bidirectional communication may be possible betweenthe ECU 46 and the processing unit 45. For example, the ECU 46 mayoutput external information such as engine parameters to the processingunit 45. Also in this case, the processing unit 45 calculates thepulsation state such as the pulsation frequency F by using the outputvalue of the sensing unit 22 instead of the external information.

As modification 9, the function achieved by the processing unit 45 maybe achieved by hardware and software, or a combination thereof. Theprocessing unit 45 may communicate with, for example, another controldevice, for example, the ECU 46, and the other control device mayexecute a part or all of the processing. When achieved by an electroniccircuit, the processing unit 45 can be achieved by a digital circuitincluding a large number of logic circuits or an analog circuit.

As modification 10, in the first embodiment, the upper extreme valuedetermination unit 56 updates the lower threshold Ee on the basis of theair flow rate, the pulsation frequency F, and the pulsation amplitudePa, but the lower threshold Ee can also be updated on the basis of atleast one of the air flow rate, the pulsation frequency F, and thepulsation amplitude Pa.

It should be appreciated that the present disclosure is not limited tothe embodiments described above and can be modified appropriately. Theembodiments above are not irrelevant to one another and can be combinedappropriately unless a combination is obviously impossible. In therespective embodiments above, it goes without saying that elementsforming the embodiments are not necessarily essential unless specifiedas being essential or deemed as being apparently essential in principle.In a case where a reference is made to the components of the respectiveembodiments as to numerical values, such as the number, values, amounts,and ranges, the components are not limited to the numerical valuesunless specified as being essential or deemed as being apparentlyessential in principle. Also, in a case where a reference is made to thecomponents of the respective embodiments above as to shapes andpositional relations, the components are not limited to the shapes andthe positional relations unless explicitly specified or limited toparticular shapes and positional relations in principle.

What is claimed is:
 1. A measurement control device comprising: asensing unit configured to output a signal according to an air flowrate; a pulsation state calculation unit configured to calculate apulsation state that is a state of pulsation generated in the air flowrate using an output value of the sensing unit; and a pulsation errorcorrection unit configured to correct the air flow rate using thepulsation state calculated by the pulsation state calculation unit,wherein the pulsation state calculation unit has an upper extreme valuedetermination unit configured to determine whether the output value hasbecome an upper extreme value of the output value when the output valueis changed from increase to decrease, and a frequency calculation unitconfigured to calculate a pulsation frequency of the pulsation generatedin the air flow rate on a basis of a time interval at which the outputvalue becomes the upper extreme value, the pulsation state including thepulsation frequency, and when the output value remains to be more than apredetermined lower threshold during a period from a timing when theupper extreme value has previously appeared to a timing when the upperextreme value has presently appeared in a waveform representing a timechange of the output value, the upper extreme value determination unitis configured to cancel the upper extreme value that has presentlyappeared, and further update the lower threshold on a basis of at leastone of the air flow rate specified on a basis of the output value, thepulsation frequency, or a pulsation amplitude specified on the basis ofthe output value.
 2. The measurement control device according to claim1, wherein the upper extreme value determination unit is configured toupdate the lower threshold using a map in which at least one of the airflow rate, the pulsation frequency, or the pulsation amplitude isassociated with a reference value of the lower threshold.
 3. Ameasurement control device comprising: a sensing unit configured tooutput a signal according to an air flow rate; a pulsation statecalculation unit configured to calculate a pulsation state that is astate of pulsation generated in the air flow rate using an output valueof the sensing unit; and a pulsation error correction unit configured tocorrect the air flow rate using the pulsation state calculated by thepulsation state calculation unit, wherein the pulsation statecalculation unit has an upper extreme value determination unitconfigured to determine whether the output value has become an upperextreme value of the output value when the output value is changed fromincrease to decrease, and a frequency calculation unit configured tocalculate a pulsation frequency of the pulsation generated in the airflow rate on a basis of a time interval at which the output valuebecomes the upper extreme value, the pulsation state including thepulsation frequency, and when the output value remains to be more than apredetermined lower threshold during a period from a timing when theupper extreme value has previously appeared to a timing when the upperextreme value has presently appeared in a waveform representing a timechange of the output value, the upper extreme value determination unitis configured to cancel the upper extreme value that has presentlyappeared, and further update the lower threshold on a basis of areference value of the lower threshold that changes according to thepulsation state.
 4. The measurement control device according to claim 3,wherein the upper extreme value determination unit is configured toupdate the lower threshold using a map in which the pulsation state isassociated with the reference value of the lower threshold.
 5. Themeasurement control device according to claim 3, wherein when the outputvalue remains to be more than a predetermined lower threshold during aperiod from a timing when the upper extreme value has previouslyappeared to a timing when the upper extreme value has presently appearedin a waveform representing a time change of the output value, the upperextreme value determination unit is configured to cancel the upperextreme value that has presently appeared, and further update the lowerthreshold by using the lower threshold used for determining the upperextreme value in a predetermined period to the timing when the upperextreme value has presently appeared.
 6. The measurement control deviceaccording to claim 5, further comprising a sampling unit configured tosample the output value at a predetermined sampling interval, whereinwhen the output value remains to be more than the lower threshold duringthe period from the timing when the upper extreme value has previouslyappeared to the timing when the upper extreme value has presentlyappeared in a waveform representing a time change of the output value,the upper extreme value determination unit is configured to cancel theupper extreme value that has presently appeared, and further update thelower threshold used to determine the output value at present time on abasis of a difference between the output value at present time sampledby the sampling unit and the lower threshold used at a time ofdetermining the output value at previous time sampled by the samplingunit.
 7. The measurement control device according to claim 1, furthercomprising a filter unit configured to remove a predetermined frequencycomponent from the signal output from the sensing unit, wherein theupper extreme value determination unit specifies the lower threshold byusing the output value of the signal transmitted through the filterunit.
 8. The measurement control device according to claim 7, whereinthe filter unit includes a low-pass filter that removes high-frequencycomponents.
 9. The measurement control device according to claim 1,wherein the frequency calculation unit has a frequency limiting functionthat limits a change amount in the pulsation frequency to be equal to orless than a predetermined maximum frequency change amount.
 10. Themeasurement control device according to claim 9, wherein the frequencycalculation unit includes an operation unit configured to set enable ordisable of the frequency limiting function.
 11. The measurement controldevice according to claim 1, wherein the frequency calculation unitcalculates a pulsation frequency average value, which is an average ofthe pulsation frequency during a predetermined period to the timing whenthe upper extreme value has presently appeared, and the pulsation errorcorrection unit is configured to correct the air flow rate using thepulsation frequency average value calculated by the frequencycalculation unit.
 12. The measurement control device according to claim1, wherein the frequency calculation unit is configured to calculate amedian value of the pulsation frequency during a predetermined period tothe timing when the upper extreme value has presently appeared, and thepulsation error correction unit is configured to correct the air flowrate using the median value of the pulsation frequency calculated by thefrequency calculation unit.
 13. The measurement control device accordingto claim 1, wherein when the upper extreme value becomes equal to orless than the lower threshold during the period from the timing when theupper extreme value has previously appeared to the timing when the upperextreme value has presently appeared in the waveform representing thetime change of the output value, the upper extreme value determinationunit is configured to cancel the upper extreme value that has presentlyappeared.
 14. A measurement control device comprising: a sensing unitconfigured to output a signal according to an air flow rate; a pulsationstate calculation unit configured to calculate a pulsation state that isa state of pulsation generated in the air flow rate using an outputvalue of the sensing unit; and a pulsation error correction unitconfigured to correct the air flow rate using the pulsation statecalculated by the pulsation state calculation unit, wherein thepulsation state calculation unit has a lower extreme value determinationunit configured to determine whether the output value has become a lowerextreme value of the output value when the output value is changed fromdecrease to increase, and when the output value remains to be less thana predetermined upper threshold during a period from a timing when thelower extreme value has previously appeared to a timing when the lowerextreme value has presently appeared in a waveform representing a timechange of the output value, the lower extreme value determination unitis configured to cancel the lower extreme value that has presentlyappeared, and further update the upper threshold on a basis of at leastone of the air flow rate, a pulsation frequency, or a pulsationamplitude which are specified on a basis of the output value.
 15. Ameasurement control device comprising: a sensing unit configured tooutput a signal according to an air flow rate; a pulsation statecalculation unit configured to calculate a pulsation state that is astate of pulsation generated in the air flow rate using an output valueof the sensing unit; and a pulsation error correction unit configured tocorrect the air flow rate using the pulsation state calculated by thepulsation state calculation unit, wherein the pulsation statecalculation unit has a lower extreme value determination unit configuredto determine whether the output value has become a lower extreme valueof the output value when the output value is changed from decrease toincrease, and a frequency calculation unit configured to calculate apulsation frequency of the pulsation generated in the air flow rate on abasis of a time interval at which the output value becomes the lowerextreme value, the pulsation state including the pulsation frequency,and when the output value remains to be less than a predetermined upperthreshold during a period from a timing when the lower extreme value haspreviously appeared to a timing when the lower extreme value haspresently appeared in a waveform representing a time change of theoutput value, the lower extreme value determination unit is configuredto cancel the lower extreme value that has presently appeared, andfurther update the upper threshold on a basis of a reference value ofthe upper threshold that changes according to the pulsation state. 16.The measurement control device according to claim 15, wherein when theoutput value remains to be less than a predetermined upper thresholdduring a period from a timing when the lower extreme value haspreviously appeared to a timing when the lower extreme value haspresently appeared in a waveform representing a time change of theoutput value, the lower extreme value determination unit is configuredto cancel the lower extreme value that has presently appeared, andfurther update the upper threshold by using the upper threshold used fordetermining the lower extreme value in a predetermined period to thetiming when the lower extreme value has presently appeared.